Showing papers in "The American Naturalist in 1936"

A Technique of Transplantation for Drosophila

Abstract: A technique of transplantation, applicable to Drosophila species, which consists of injection by means of a micro-pipette, is described in some detail.

A Developmental Analysis of Inherited Shape Differences in Cucurbit Fruits

Abstract: Fruit shape in the Cucurbitaceae is inherited, and there are at least four quite distinct types of shape determination, as follows: (1) Differences in shape index (ratio of length to width) which are established in the earliest visible primordia and may persist unchanged throughout development. (2) Constant differences in growth rate between length and width which occur during the entire course of development, causing a progressive change in index. The relative growth of these two dimensions may be measured by a constant. In the types studied this varies from .8 (length growing .8 times as fast as width) to 2.2 (length growing 2.2 times as fast as width). (3) Differences in shape index at maturity which necessarily result from differences in size in all cases where the relative-growth constant is other than 1. Where shape index is progressively changing, the point at which growth of fruit stops (its mature size) will affect its index. (4) Differences in pattern or profile, which are more complex than thos...

Isolation and Growth Characteristics of the "Zoochlorella" of Paramecium bursaria

Abstract: attachments appear between chromatids of the same pair of homologues, but at higher doses there are interchromosomal attachments as well.) A series of glands from larvae irradiated with 50r. to 500r. at 6 to 8 hours (25? C.) showed no translocations. The chromatic and interbandular deficiencies occur with low frequency, only occasional chromosomes in some of the glands showing them, similarly, in Gasteria induced chromosome attachments and breaks are much more frequent than chromatic deficiencies (achromatic spots in the chromonema) (Marshak, 1935). We may conclude therefore that the fundamental structure of the chromosomes is essentially the same in both forms. More data are necessary before an exact quantitative comparison can be made. However, if the gene be identified with the self-reproducing unit of the chromonema, the results thus far obtained indicate that in the chromosomes of the Drosophila salivary gland it is located on the chromonema in the region between chromioles or chromomeres. ALFRED MARSHAK

Observations on the Species Related to New Forms of Drosophila affinis, with Descriptions of Seven

Abstract: Drosophila affints Sturtevant (1916, p. 334) has been recorded from many localities, railging from New Hampshire and Illinois, south to Florida and west to Texas and Kansas (Sturtevant, 1921). We find that there are forms in Alaska, the northwestern IJnitecl States and the Mexicall plateau that also will fit the published descriptions of affinis; but these represent distinct species, and careful study shows that the original material is itself a mixture of several species. The members of this group are clearly closely related to the forms that have gone under the name of Drosophila obscura. This is also a complex group, containing at least four European species and the western American Drosophila pseudloobscura (Frolowa and Astaurow, 1929) and Drosophila miralnda (Dobzhansky, 1935).

Water Absorption by Reptile Eggs during Incubation

Abstract: Other red-shafted characteristics would appear only when the hybrids mated. It can be noted that the hybrid parents of family 2 gave young which are predominantly of the yellow-shafted type. Taxonoinically, some confusion is likely to occur, due to mutations or hybridization, as among the flickers, when the criterion of specific status is largely that of plumage color. A review of the various species criteria and a discussion of the species problem are given by Robson (1928). In this sample of flickers are seen the possibilities through segregation of the subspeciation of hybrid types possessing any combination of the characteristics of the two species; such events must have occurred often during the species diversification of woodpeckers. However, this is not likely to occur to any perceptible extent, owing to the migratory habits of the birds and the absence of effective geographical barriers. Moreover, none of the various plumage characteristics appear to offer any particular advantage either as protective coloration or in sexual selection. Indeed, the evidence would indicate that hybrids possess an advantage, at least with the redshafted species, probably due to the increased vigor that usually accompanies hybridity.

The Food of Insects and its Relation to Resistance of Plants to Insect Attack

Abstract: A STUDY of the resistance of crop plants to insect attack has served to emphasize the great importance of food habits in the biology and evolution of plant-feeding insects. The evidence is accumulating that two plants, identical outwardly, may differ widely in nutritive value to an insect species as measured by the insect's ability to maintain a population on them. Resistance of plants to insect attack may be defined as the relative amount of qualities possessed by the plant which influence the ultimate degree of damage done. For practical purposes it represents the ability of a crop plant to produce a larger crop than do ordinary varieties at the same level of insect population. This difference in yield is a measure of the economic value of resistance, but is, however, dependent on many factors as well as resistance to insects. It should be the purpose of projects on insect resistance in crop plants to produce varieties not only as good or better in respect to agronomic characters and disease resistance than those now available, but also resistant to one or more insects. Thus the breeding of crop plants resistant to insect attack becomes part of the entomologist's contribution to the crop improvement program of a particular crop and, conversely, insect resistance should

The Sex-Determining Mechanism of Drosophila miranda

Abstract: DOBZHANSKY1 has discovered in Drosophila miranda a remarkable new system of sex determination which has presumably been derived from the XY system found in all its immediate relatives. Its character is important, therefore, in showing not only a new method but also an evolutionary change of method. Dobzhansky shows clearly that this species has an X-O mechanism like that of Orthoptera and that this mechanism is superimposed on the older XY mechanism. He is led to assume, however, that both are effective in sex determination. There is then an X2_0 segregation conibineci, and, what is more, correlated, with X'-Y seoreoation; X1 and X2 although unconnected go to the same pole. This is a drastic assumption, as Dobzhansky recognizes. It almost uproots genetics. But there is an alternative that seems to fit the published evidence equally well, as follows: (1) The X1-Y pair is effectively homozygous with regard to sex. It contains a middle \"pairino segment,\" derived from the type of presumably homozygons pairing segment of X-Y in other species, while its arms are derived partly from autosomes and partly from sex-indifferent parts of X and Y. Differences in size between the paired chromosomes are due to structural changes having no relation to sex. (2) The X2 chromosome contains the sex-differential part of the X chromosome of the other species. It has possibly taken its attachment chromomere by interchange from the fourth chromosome. (3) The essential sex-mechanism is therefore X-O. The pairino segments of X1-Y still show the special pairing mechanism by reciprocal chiasmata found in X and Y of the other species and a failure of pairing in the salivary glands. The displaced mechanism survives its use. This it should do, in my view,2 even if the pair are homozygous, since the mechanism is a genotypically controlled property of the pairing segments of these chromosomes. These segments would be expected to survive structural changes 1 Tl. Dobzliallsky, Genetics, 20: 377-391, 1935.

Genetic Aspects of Certain Problems of Evolution

Abstract: THERE is a general feeling among specialists in other departments of biology that the geneticist has made no contributions toward the solution of the more general problems of species origin. These biologists are evolutionists-but merely because the wealth of circumstantial evidence presented by Darwin makes the notion plausible, and because all facts discovered later are consistent with the idea. The whole concept remains for them, in form and factual content, just as outlined by the author of the \"Origin of Species,\" with perhaps more precise information on the subject of variation, with somewhat more exact knowledge of the laws of inheritance and with certain changes in the values allotted to such factors as acquirements, mimicry, hybridization, isolation, and the like. Few would grant that ideas as to the methodology of evolution are substantially clearer now than they were seventy-five years ago. Such a position is not consistent with the facts. The most important single obstacle in the path of Darwin's rationalization of the evolution process was the current reliance on the principle of blending inheritance. During the first third of the present century, this impediment was disintegrated and swept away. The establishment of the particulate theory of inheritance, with units of heredity arranged in linear fashion in the chromosomes and distributed by definite laws, has made it possible to calculate precisely what must happen to a given population under any particular system of breeding, when the type of chromosome mechanism existing in the population is known. And the chromosome mechanisms have

The Relation between b and k in Systems of Relative Growth Functions of the Form y = bxk

Abstract: Biitschli, 0. 1880-82. "Klassen und Ordnungen des Tierreiches." Bd. 1, III. DeBary, A. 1879. 'Die Erseheinung der Symbiose.' Strasburg. Entz, G. 1881-82. Biol. Zentralbl., 1: 646. Hood, C. L. 1927. Biol. Bull., 52: 79. LeDantee, F. 1892. Ann. lust. Pasteur, 6: 190. Loefer, J. B. 1934. Science, 80: 206. 1934a. Biol. Bull., 66: 1. 1936. Jour. Exp. Zool., 72: 3. Loefer, J. B. and R. P. Hall 1936. Arch. f. Prot. (in press). Oehler, R. 1922. Arb. a. d. Staatsinst. f. exp. Ther. u. d. Geory Speyer-Haus, 15: 5. Jena. Pringsheim, E. G. 1928. Arch. f. Prot., 64: 289. von Siebold, C. T. 1849. Zeitschr. f. wiss. Zool., 1: 274.

A Single Theory for the Physiology of Development and Genetics

Abstract: (1) It is held that the apparent irreconcilability between physiology of development and genetics does not mean that they actually are separate. They are regarded as two aspects of development and the data of both are accepted. However, the now more prevailing theory of embryonic segregation, and with it all theories of embryonic segregation, and the gene-theory of heredity are rejected as explanations for the physiology of development. (2) Instead of any theory of a segregation, a theory of genetic restriction is proposed, in which it is postulated that the egg from its fertilizable condition, when it has capacity for the production of many embryos, is steadily restricted in its potencies. From a condition of pluripotency it becomes unipotent; then the blastomeres of this unipotent system with first cleavage or thereafter, depending upon the species of egg, become farther restricted and now give rise only to certain areas of the embryo. The loss of potencies is correlated with the increase of nuclear mat...

On the Meaning and Limits of Irreversibility of Evolution

Abstract: THE Law of Irreversibility of Evolution was first promulgated in 1890 by the late Louis Dollo, of the Musee Royale d 'Histoire Naturelle of Belgium, and was developed by him in various later papers, especially in 1890, 1892, 1893 1905, 1922. It was named Dollo 's Law by his distiiiguishecl pupil and chief exponent, Othenio Abel, of Vienna. According to Dollo the irreversibility of evolution is due to the irrevocability of the past. He held that when in the course of evolution an organ or a part is lost, that same organ or part is never regained, although a substitute for it may be found if the need arises. Heredity and variation, he said, are unceasing and opposing forces. If, after all organ had disappeared, heredity alone were to continue, the organ might conceivably reappear; but since variation is always operative to a greater or less extent, a complete return to an earlier stage is impossible. So-called "reversions," as in the case of modern threetoed horses, did not constitute in Dollo 's eyes a real exception to the law of irreversibility, since, as we shall see later, 'reversions'' may be accounted for in ways not incompatible with irreversibility. The adaptability of living matter to changing ellvironmental conditions or to changing opportunities was to Dollo axiomatic. But his theory of irreversibility will work just as well if we accept the theory of preadaptation as advocated independently by Cuenot and Davenport, which is that structural changes in evolution take place

Hybrid Vigor in Maize

Abstract: E. W. LINDSTROM has published in this journal (19355) a socalled \"test of the Ashby hypothesis of heterosis,\" which calls for some comment. The present writer has made two contributions to the problem of hybrid vigor in maize (1930, 1932). Neither of these contributions contains any hypothesis, but certain data are presented, the interpretation of which is selfevident. The data were obtained from experiments in which populations of two inbred lines of maize and the F1 between them were grown side by side in the same environment. The populations were sampled during growth over a period of 83 days, and from these samples the relative growth rates expressed as dry-weight increase were obtained. Size-heterosis was apparent from the outset, and after 70 days' growth the dry weight of the hybrid was four times that of the heavier parent. Nevertheless, analysis of the data showed that the relative growth rate of the hybrid did not exceed that of its parents, but the higher parental growth rate was inherited as a complete dominant. The final size of a plant is the resultant of the initial size of its primordia and the relative growth rate. Since in relative growth rate the hybrid had no advantage over its parents, sizeheterosis must have been due to an initially bigger primordium. In other words, if the rate of compound interest in the hybrid is no bigger, its capital of dividing cells must be higher.' The simplest way to measure this capital is to dissect the primordia (plumule and radicle) from the embryo and weigh them. When this was done it was found that the hybrid embryos were bigger than those of either parent, and the 'size-heterosis observed in these experiments was due solely to the maintenance of this initial advantage in primordial size. The experiments were repeated in Chicago with other strains of maize, and have since been repeated with beans and six strains of tomatoes, with the same results.

On the Variability of Mixed Races

Abstract: IN 1927 Herskovits called attention to the important fact that the American Negro population studied by him did Rot lhave an appreciably greater variability in respect to most characters than did populations of whites and African Negroes related to those wiich had gone to form the mixed group. The mixed group in question was probably derived to the extent of at least 20 per cent. (possibly much more) from Cancasian stocks, and also had a small indeterminable amount of American Indian admixture. The mixed group was roughly divided by him into several subgroups, according to the relative proportions in which the two races had entered into the individual 's composition (as determined by questions concerning the individual's ancestry) and in each of the subgroups (even in that consisting of more nearly 50 per cent. from each of the two races chiefly concerned) the low variabilitv was found. Herskovits concluded that \"the :Mendelian mechanism of heredity, if operative at all in this population, is obscured by complicating factors.'\" He was inclined to think that through the process of repeated breeding of the members of the mixed race amongst one another, a, trne new race of intermediate type had become established, the stability of which was quantitatively similar, and (presumably) similar in its basis to the stability of the original races. In a more

The "Myth" of the Lemur's Comb

Abstract: anatomy, these procumbent lower anteriors have been cited as a classic example of dental specialization. They have also stimulated interest because of the difficulty in identifying the cuspid and the first premolar in position. Writings on the lemuroid dentition, however, center about the latter question.; namely, as to whether the outermost members of the series of the teeth of the comb represent hird incisors or modified cuspids. The possibility that these teeth might not be a comb at all has not been suspected. In the lemur, the six lower anterior teeth extend hori-zontally forward (Fig. 2). The canine has entered the

The Non-Identity of the Neurohumors for the Melanophores and the Xanthophores of Fundulus

Abstract: IT has been shown that the reactions of the xanthophores (yellow pigment cells) in Fundulus heteroclitus are independent of the responses of the melanophoresblack pigment cells (Connolly, 1925; Fries, 1931). For example, both the xanthophores and the melanlophores are contracted in a fish which has been kept for some time in an illuminated white vessel, and both are expanded in one kept in an illuminated black vessel. In an animal adapted to a blue background, however, the melanophores are mainly expanded and the xanthophores contracted, while on a yellow background, the xanthophores are expanded and the melanophores are contracted. Thus this inclependent behavior of the yellow and black pigment cells to yellow and blue backgrounds led Fries to conclude that the two types of chromatophores were controlled by separate sets of neurons. In the following year, Parker (1932) formulated the neurohumoral hypothesis for the control of chromatophores on the basis of the responses of denervated melanophores. Such responses were first clearly described by Fries (1931), who declared that they must be governed by humoral substances. Mills (1932), who studied in detail the same responses, concluded also that humoral factors were responsible for the activity of enervated melanophores and stated further that these humoral substances were secretions from intact nerve terminals surrounding 1 These experiments were performed at the Marine Biological Laboratory, Woods Hole, Massachusetts, during the summers of 1934 and 1935. For the privilege of working at the laboratory in 1935, I am especially indebted to its director, Dr. M. H. Jacobs.

Litters from Ferrets in January Induced by Increased Exposures to Light After Nightfall

Abstract: (1) Three ferrets were induced to come into oestrus in November, December and January by graduated increases in daily exposure to electric light after nightfall. (2) They were mated once each with males rendered sexually active in the same way, and two became pregnant, the other only pseudopregnant. (3) One of the pregnant females gave birth to a litter of six on January 14; the other died before parturition. (4) The birth of this litter indicates that both male and female ferrets, brought into sexual activity in winter by increasing exposures to light, are potent and fertile, and can produce young under conditions of temperature in which newly born ferrets were unable to survive. (5) In each of these females winter coat was shed, beginning about two weeks before the expiration of term, and summer or spring nursing coat was completed after the termination of pregnancy or pseudopregnancy. (6) It is suggested that numerous copulations within thirty hours may possibly cause luteinization of ovarian follicles...

Structural and Chemical Aspects of Animal Coloration

Abstract: COLORS have always exerted an attraction for artists, scientists, laymen and savages alike the world over, and chromiatology finds very real and wide use both in various pure sciences and in such applied fields as those of agriculture, certain industries and medicine. The experiniental or practical geneticist who may be concerned with the inheritance of any of various color manifestations is really studying the heritability of certain definite kinds of metabolic processes; likewise the physician, who bases many of his diagnostic conclusions upon the colors of tissues, other structures and body fluids, is scrutinizing the signposts of various normal or aberrant metabolic functions. The colors manifested by animal organisms may be structural or pigmentary, and of the latter, either enidogenous or exogenous, i.e., derived either metabolically or from plant food, directly or indirectly. We are reminded (Wood, 1934) that \" opaque substances are seen by the light reflected from their surfaces; transparent substances in part by reflected light and in part by transmitted light,\" and that \"the colors of most natural objects result from absorption.\" Incident light, penetrating to a greater or less degree the surface of an object, undergoes reflections, diffractions or refractions as it strikes minute internal structures; the absorbed rays which are totally reflected or refracted ill the interior of a body, do not reappear but are converted into heat, while the residual light emerges minus these most strongly absorbed rays and waTe say that the object has a certain color. The principle of selective absorption of various constituent rays of white light holds, whether the re1 Presented at a symposium on ' Color in Animals ' of the Western Society of Naturalists, Stanford University, December 27, 1935.

The Phylogeny of the Adrenal Gland

Abstract: INTRODUCTION BEFORE discussing the mammalian adrenal on which this paper is based, I find it necessary to give a brief recapitulation of our knowledge of the adrenal in the lower Vertebrates. No adrenal homologues are found in Amphi oxus nor is there any comparable structure in the Ascidians, although these animals possess in the neural gland a structure which is really a rudimentary pituitary gland. With regard to Invertebrates, Gaskell (1912) and Poll (1906) have found bodies whicli they consider the equivalent of the adrenal medulla in the body cavity of the leech Hirudo medicinalis, but no similar bodies have been found in any other Invertebrates. In the next Vertebrate group we come to the Cyclostomata-the pro-fishes, or lampreys, and of these, Giacomini (1902, 1912) has described two series of bodies in Petromyzon, one series irregular in shape, which are attached to the walls of the posterior cardinal veins, the renal arteries and the arteries dorsal in position to the kidney. These are the representatives of the cortexthe cortical or inter-renal bodies. The second series are in the form of strands of tissue running along the large arteries and extending practically the whole length of the body cavity. These are the representatives of the chromaffin tissues of the higher forms. -In Bdellostoma so far only the chromaffin tissue has been found, the cortical tissue is no doubt present, but is 1 Read to the Zoology Section of the Australian and New Zealand Association for the Advancemeat of Science, Melbourne, January, 1935.

A Frequently Mutating Gene in the Pineapple Ananas Comosus (L.) Merr

Abstract: The spiny-leaved plants and the spiny-smooth chimera plants which are found in Cayenne fields originate as somatic mutations. The percentage of chimera plants was found to be smaller in the Cayenne variety, which genetic tests had indicated as being hybrid for spiny leaves, than in smooth-leaved hybrid plants produced by crossing smooth-leaved with spiny-leaved varieties. This difference, it is believed, may be due to homozygous smooth-leaved plants in the Cayenne population which do not produce chimeras. A clon derived from a hybrid plant homozygous for smooth leaves contained no chimeras when a similar sized population of heterozygous plants would have contained 43 chimeras. A method is outlined by which homozygous Cayenne plants can be identified if they exist in the variety. The rate of mutation from smooth to spiny in the pineapple, 4.95 per cent., places this in the category of frequently mutating or unstable genes.

Heterokaryosis and Hormones in Neurospora

Abstract: a very ineffectual part as predators. Here, then, is an example of negative natural selection where the survival of the fittest, owing to the elimination of the less fit, is practically non-existent. Oceanic islands are of great interest to the zoogeographers because of a number of characteristics, one of them being the presence of peculiar animals which usually occur nowhere else. The faunal peculiarities of these islands may be partially explained on the basis that the environment is such as to permit animals with unusual characteristics to persist because predatory animals, which elsewhere would eliminate them shortly after they appeared, are absent. Further, as a result of inbreeding, these unusual characters tend to be disseminated among a greater number of individuals on an island, so that any recessives, such as albinism, would have a greater possibility of appearing than they would among a similar population on a continent. These environmental and genetic characteristics are present on Lanai, so that here a unique example of the m'itodus operadli in the evolution of an oceanic island fauna is available for study.

Natural Hybridization and Genetics of Flickers (Colaptes)

Abstract: ON the North American Continent the two common species of Colaptes, a genus of the woodpecker family, are C. atratus, or the yellow-shafted flicker, and C. cafer, or red-shafted. That hybridization occurs on a grand scale between these two species was, according to Allen (1892), first pointed out by Baird in 1858. A very good account of the relationship between these two species is given in Allen's paper. The geographical area of active hybriclization is given as extending from southeastern Texas northward along the western edoe of the Plains into Canada and thence westward to the coast a belt of country estimated from 300 to 400 miles wide and some 1,200 to 1,500 miles long. Recently Taverner (1934) gave a more detailed account of the geographical extent of hybridization in Canada based upon the collection in the National Museum, Ottawa. This collection now consists of 166 flickers. Of these 115 specimens were collected from 21 localities westward of Manitoba to the coast, including Wood Buffalo Park, southern Alaska and Vancouver and Queen Charlotte Islands. Of these 60 are hybrids, 37 are redand 18 yellowshafted. The remaining 51, which are pure yellow-shafted, were collected from various localities eastward of the SaskatchewanManitoba boundary to the Atlantic. The present paper deals with a genetic study of these flickers and made on the suggestion and through the courteous assistance of Mr. P. A. Taverner. The hybridization of these two species is of interest taxonomically because of the possibilities of the ultimate hybridization in some decree of the red-shafted species and the latent possibilities of subspeciation of hybrid types. Genetically they are of interest because they possess five contrasting plumage characteristics. Four of these are given in Table 1 for both species and hybrid together with the postulated genotypes. The fifth characteristic, namely, gray or brown crown plumage color, is not given because it did not appear to be a reliable characteristic in young birds. The hybrid birds were classified by inspection according to the per cent. presence of yellow-shafted characteristics, with the exception of wing and tail color. The results are given in Tables 2 and 3. Table 2 consists of two families of hybrid parents and

The Statistical Analysis of the Distribution of Pond Molluscs in Western Canada

Abstract: THE following account dea]s with the distribution of fresh-water mollusca in the western part of Canada, and consists of the results of the study of the fauna of 315 ponds and small lakes. It was considered desirable to make a more precise analysis of their molluscan fauna, from the standpoint of local and geographical distribution, than has previously been attempted with any group of invertebrate animals. The use of statistical methods has led to important advances in plant geography, and it is believed that the following pages, which are to be regarded only as a preliminary essay, will indicate that when carried out in more detail, equally interesting results will come from the application of such methods to the study of animal distribution. Nearly thirty years ago Forbes (1907) formulated a method of obtaining a measure of the association of one species with another, but unfortunately he utilized it in the study of a group of fishes, the Etheostominae, to which it was not particularly well adapted. Since Forbes's work was published the method seems to have been forgotten; at any rate very few references to it are to be found in the literature. The point of view taken here is an extension of that of Forbes. Most data on geographical distribution are not adapted to statistical analysis. The collecting is done in a more or less haphazard fashion; collecting places are widely and unevenly scattered in space and time; and the number of observations is usually inadequate. The result is a heterogeneous mass of material which can not be handled mathematically. Effort has been specially di-

Linkage Relations of Crest, Dominant White and Frizzling in the Fowl

Abstract: The data here presented definitely establish the fact that crest, dominant white and frizzling belong to the same linkage group. It is shown that these genes have the arrangement in the chromosome of Cr-I-F with approximately 12 per cent. crossing-over between Cr and I and 17 per cent. between I and F. Since the percentage of crossing-over between Cr and F is 29, the distance in the chromosome between Cr and F, as measured by the summation of the segments Cr to I and I to F, is practically identical with that secured by directly measuring the percentage of crossing-over between Cr and F. This indicates that little double crossing-over occurs in the approximate distance of 29 units on this chromosome. In segregation of these genes in birds heterozygous for all three, no double cross-overs were recorded in 284 gametes. Evidence is adduced to support the view that cerebral hernia is ordinarily the homozygous expression of crest, but a number of irregularities were found in the manifestation of cerebral herni...

Genetics and Ontogeny

Abstract: PERHAPS the greatest mystery which the experimental embryologist encountered in the early period of his science was the fact that isolated parts of a developing individual could give rise to whole individuals. How it was possible for living wholes to be separated into pieces and to enable the pieces to become wholes of the same kind as the original seemed to be the question of life's nature itself. In a certain way this question has been answered by genetics. If the nucleus of the fertilized egg contains the full set of determiners for the developing whole organism and if there is an equal division of all determiners, so that all cells obtain the full set of them, then the mystery of the isolated parts being able to become equal to the whole ceases to be a mystery. But here the new problem awaits us. If each cell encloses the same whole group of determiners, how is it possible that in the developing whole that process takes place which is one of the fundamentals of ontogeny, namely, differentiation? This question is fully justified. To account for differential development in different parts of the embryo we need more than an unchanging set of genes. If the agent, the genes, is unchanged in different parts of the embryo, then the reagent, the plasma, must be diversified. Thus the nature of the non-genic differences between different cells of the developing embryo would be the problem of ontogeny. We know very little about the nature of these differences. To account for their origin it is necessary to assume a diversification of plasmatic regions already in the undivided egg. This enables the division products of the nuclei to segregate into cells with qualitatively or quantitatively different plasmatic content. The result is a primary potential cellular differentiation i spite of the assumed genetic identity. How further differentiation, the production of new differences, not only the cellular segregation of preformed ones, originates can be imagined easily. The position of every part in the diversi-

Comparative study of four high tumor lines of mice.

Abstract: (1) The "D" strain. The animals of this strain are descended from the Little dilute brown race. They have been inbred by brother-to-sister matings since 1909. The diet which this strain received consisted of hemp and canary seed, cod liver oil puppy cakes and milk. Lettuce or cabbage was given once a week. The breeding and tumor observations have previously been reported for this stock by Murray (4). (2) The "A" strain. This strain originated from the Bagg albino stock, being inbred since 1912. Prior to 1932 the food which the animals received was a mixture of rolled oats, powdered milk, powdered meat scraps and salt; cod liver oil puppy cakes and water, with lettuce or cabbage being added once a week. Since 1932 the animals have had Purina Fox Chow and water. For simplicity, the line of the A stock which received the rolled oats diet shall be termed the A-RO line and the other the A-PC line. The number of animals which developed spontaneous mammary gland tumors in two other lines of the A stock has been reported by Strong (5). The number of individuals dying from other causes than cancer was not given. Thus the data observed by Strong can not be compared with that recorded in this report.

The Structure of the Chromosomes of the Salivary Gland of Drosophila melanogaster

Abstract: off their leaves above the growing point; and despite this mutilation the hybrids exceeded their parents in final size and in yield. It is obvious that no relevant evidence can be obtained by removing indiscriminately the organs of a plant as \"capital.\" There is no comparison between \"capital\" as number of cells in the primordium and \"capital\" as the amount of non-meristematic leaf material. Had Lindstrom removed the flower buds, the \"capital,\" in his sense, would have been reduced negligibly, but the yield would have fallen to zero. That removal of the photosynthetic organs stimulated vegetative vigor is in accordance with the classical work of Kraus and Kraybill (1918). It is a physiological response; and rather than being inconsistent with the author's work, it is irrelevant to that work.

Chromosome Structure in Tradescantiae. VII. Further Observations on the Direction of Coiling in Tradescantia reflexa Raf

Abstract: In an x-rayed strain of T. reflexa showing rings or chains of two, four and six chromosomes, respectively, serial observations indicate that the direction of coiling tends to fall into certain patterns within a given half-anther. These patterns do not necessarily belong to given chromosomes or parts of chromosomes but appear to belong to a given group of chromosomes. Random coiling is thus considered to be modified within an anther. Similarity of patterning between half-anthers is suggested, but over a long period and with a sufficient number of observations the various patterns between different anthers may form a random series.