THE author of this book ranks as the foremost American worker on insect morphology. His contributions on the subject are notable for their clarity and originality of thought, and the appearance of a volume, embodying his ideas in comprehensive form, is sure of a hearty welcome. In its preparation, Mr. Snodgrass has incorporated the results of much first-hand study with those of many recent investigators in the same field. He has produced an outstanding book wherein knowledge of facts is combined with that of function and, at the same time, theoretical conceptions of the origins and relationships of organs and parts are not overlooked. Principles of Insect Morphology
 By R. E. Snodgrass. (McGraw-Hill Publications in the Zoological Sciences.) Pp. ix + 667. (New York and London: McGraw-Hill Book Co., Inc., 1935.) 36s. net.

Principles of Insect Morphology

In insects, accumulation of yolk, or vitellogenesis, is a heterosynthetic pro­ cess, in which an extraovarian tissue, the fat body, produces yolk protein precursors ( 1 , 92). Heterosynthetic vitellogenesis occurs even in the most primitive insects, the Apterygota (9, 10, 1 13). Only for two apterygote insects have ultrastructural observations indicated participation of autosynthesis in vitellogensis (9, 10) . This claim, however, requires confirmation by biochem­ ical or immunochemical means . Because of the heterosynthetic nature of vitellogenesis in insects, their oocytes are highly specialized for the specific accumulation of extraovarian yolk protein precursors . Telfer first implicated the role of endocytosis in yolk deposition in insect oocytes . He found selective concentration of some hemolymph-borne proteins in yolk bodies of Hyalophora cecropia oocytes ( 1 29, 1 3 1 ) . Coated vesicles, the cellular structures associated with selective endocytosis, were first observed in oocytes of the mosquito Aedes aegypti ( 1 1 2) . These pioneering studies were followed by numerous electron micro­ scopical and tracer investigations that supported earlier data on the in­ ternalization pathway of extraovarian proteins in follicles and on the role of coated vesicles in yolk deposition in insect oocytes (reviewed in 1 33) .

Accumulation of yolk proteins in insect oocytes

Publisher Summary Among animal hormones, juvenile hormone (JH) is distinctive because of its unique structure and the diversity of its effects on insect development and reproduction. This chapter reviews the actions of JH on the fat body, gonads, accessory glands, muscle, and nervous system of adult insects. Whereas the epidermis is a major target of premetamorphic JH action, it has been studied little in adult insects, which generally do not moult. However, since the development of yellow pigmentation that accompanies sexual maturation in adult male locusts is clearly dependent on JH-regulation processes, in which cellular and molecular mechanism are investigated. The rapid recent progress in understanding how ecdysteroids regulate the gene activities has resulted from the opportunities afforded by drosophila melanogaster: mapped and characterized mutants, polytene chromosomes with puffs marking active genes, efficient germ-line transformation. The recognition of two aspects of JH action in the tissues of adult insects is reviewed. A model for understanding some aspects of priming by JH may be found in the action of ecdysteroids, where early genes produce factors needed for the expression of late genes. In structure, thyroxine is very different from JH, but there is considerable resemblance between thyroxine and phenoxyphenoxy carbamate, fenoxycarb. Functionally, there are marked similarities. Thyroxine governs metamorphosis in amphibians, but is remarkably pleiotropic in governing many processes ranging from the maturation of the central nervous system to thermoregulation. The chapter emphasizes the importance of selecting insect systems on the basis of their optimal features for research, rather than historical precedent or economic importance. With selection of appropriate systems and application of the cell and molecular research techniques now available, the elusive problem of JH action should soon yield to enlightenment.

Cellular and Molecular Actions of Juvenile Hormone. II. Roles of Juvenile Hormone in Adult Insects

Phylogeny is evolutionary interrelationship expressed in terms of recency of common ancestry. The elaboration of the theoretical framework of phylogenetic systematics ("cladistics") by the Hennig school [(e.g. 34, 35); for an introduction to later developments see (5)] has led to an upsurge of interest in reconstruction of phylogenies and has proved particularly stimu­ lating for inquiries into concepts of interrelationships of higher categories. This review is devoted to a treatment of the phylogeny of extant orders of insects and their closest relatives. Palaeozoic hexapods are reviewed by Wootton in this volume. The "ordinal" level has been fixed largely by convention within each major group in the Animal Kingdom. The orders recognized here are presented in Figure 1. These taxa are obviously not equivalent by any criteria, but at least it can be argued that they are all monophyletic entities. A comprehensive treatise on the phylogeny of higher hexapod categories, including lengthy discussions of previous hypotheses, was published in 1969 by Hennig (35). Hennig's views were subsequently critically assessed by Kristensen (43) with reference to a substantial amount of additional evi­ dence. These two works provide extensive bibliographies and are referred to repeatedly throughout this review. Emphasis is laid on a presentation of current views, and particular consideration is given to the numerous new proposals made in a thought-provoking, recent book by Boudreaux (15).

Phylogeny of Insect Orders

Publisher Summary This chapter discusses the structure and regulation of the corpus allatum. The corpora allata (CA) are endocrine glands in the posterior regions of the head, or in rare instances in the thorax, which are closely associated with the stomatogastric nervous system. This chapter focuses on the regulation of the CA. It also describes the embryology, innervations, and the relationships of the structure, particularly the ultrastructure, to its synthetic activity. The characteristic shape of the CA is ovoid to round but they may be elongate as in large larvae and adults of Libellula depressa. The size of the glands is frequently about the diameter of the aorta or smaller; however, there is much variation among species and even within a species, size differs with age, sex, polymorphism, and the activity cycle of the glands. Although only one type of glandular cell occurs in the CA, there are a variety of types of CA with respect to the number of cells per gland and the relative size of the cells. The CA are surrounded by a continuous noncellular basal lamina, roughly 0.1-1 μ m thick. This material occasionally projects between two glandular cells into the interior of the gland, forming trabeculae that may accompany nerves and trachea.

Structure and Regulation of the Corpus Allatum

A detailed description and a morphological interpretation of the VIIIth and the IXth abdominal segments of the female machilids is given in this paper. The median gonopore is situated in the posterior part of the VIIth segment and followed in the VIIIth segment by a sagittal cleft in which open 2 pairs of receptacula seminis. The VIIIth sternite is reduced to a transverse bar bearing the insertions of the anterior arms of the endosternites. In the IXth segment the sternal area is entirely membranous, but there is also a transverse bridge which we interpret as resulting from the union of 2 sclerites detached from the anterior part of the coxites. The large gonocoxites IX delimit a genital chamber in which are placed the gonapophyses bases. At the latero-anterior part of each IXth gonocoxite there is also a little sclerite, the laterocoxite or gonangulum, which probably corresponds to the second valvifer of the orthopteroids. The morphological value of the 2 pairs of gonapophyses is then discussed; we believe that these formations are coxalia interna carried by an area homologous to this, which gives rise to the eversible sacs in the pregenital segments.

Morphologie abdominale des machilides (Thysanura)—II. Squelette et musculature des segments génitaux femelles

During the period between apolysis and ecdysis, the vesicular glands show many important transformations which affect not only the cuticular ductules, but all the cells. The cytoplasm of the glandular cells undergoes a partial autolysis, whereas other parts of the cells present a high secretory activity. Immediately after the apolysis the cellular reservoir empties and disappears almost completely; soon after, refills with secretion. The most interesting transformations concern each ciliary cell, always associated with a glandular cell. In the first phase of the moulting cycle, the dendrite of the ciliary cell grows a ciliumlike extension (= distal region of the dendrite), which penetrates into the corresponding ductule; the new intima of this ductule is laid around the cilium. At the same time, the proximal region of the dendrite forms a circular fold around the base of the cilium and begins to secrete a material which will form the end apparatus. This latter is finished during the second phase of the cycle. The third phase is characterized by the degeneration of the distal region of the dendrite and the circular fold. Thus, the end apparatus is not a secretion of the ductule-carrying cell, but of the ciliary cell. At the end of the moulting period, just before ecdysis, the vesicular gland again takes the structure characteristic of the intermoult: the reservoir of the glandular cell is very large; the cuticular apparatus is almost formed; the dendrite of the ciliary cells shows, at its apex, a short “cilium” (= ciliary region s. str. + short distal region) surrounded by microvilli, free in the secretion of the reservoir.

Modifications ultrastructurales des glandes vésiculaires des Machilidae (Insecta, Thysanura) au cours des cycles de mue

Les Machilides presentent une serie de vesicules abdominales paires, sous forme de sacs exsertiles capables d'absorber l'eau d'un film liquide. Les coupes histologiques montrent qu'une partie de la paroi de ces vesicules est faite d'un epithelium particulier revetu d'une intima cuticulaire plus epaisse que celle de l'epithelium banal. La microscopie electronique permet de preciser la structure des cellules absorbantes qui sont caracterises essentiellement par des microvillosites apicales et de profondes invaginations de la membrane plasmique basale associees a des mitochondries allongees. Une comparison est faite avec d'autres types de cellules absorbantes connues chez les Arthropodes, notamment dans le rectum. Grâce a leurs vesicules abdominales, les Thysanoures possedent des organes originaux jouant un role important dans l'equilibre hydrique de ces insectes.

[The absorbing epithelium of abdominal vesicles in Machilida (Insecta Thysanura) histology and ultrastructure (author's transl)].

Antigonadotropic and antiallatal effects of precocene II in the firebrat, Thermobia domestica (Thysanura, Lepismatidae)

During courtship, males of Chrysopa perla extrude from the genital aperture two eversible vesicles that bear approximately 50 sclerotized tubercles with a long, apical hair. Ultrastructural study reveals within each tubercle two juxtaposed subunits: a sensory subunit formed by a mechanoreceptor neuron, a glial cell, two enveloping cells, and a glandular subunit consisting of a glandular cell provided with an extracellular reservoir, a duct cell and an enveloping cell. The glandular-cell cytoplasm is characterized by extensive RER, a large amount of SER, probably involved in lipid elaboration, and voluminous myeloid bodies encircling the reservoir. The secretion is released to the outside by a cuticular duct that opens into the side of the tubercle. The function of the mechanoreceptor associated with the glandular subunit is discussed.

Jacques Bitsch

Papers

Morphologie abdominale des machilides (Thysanura)—II. Squelette et musculature des segments génitaux femelles

Modifications ultrastructurales des glandes vésiculaires des Machilidae (Insecta, Thysanura) au cours des cycles de mue

[The absorbing epithelium of abdominal vesicles in Machilida (Insecta Thysanura) histology and ultrastructure (author's transl)].

Antigonadotropic and antiallatal effects of precocene II in the firebrat, Thermobia domestica (Thysanura, Lepismatidae)

Ultrastructure of pheromone-producing eversible vesicles in males of Chrysopa perla L. (Insecta, Neuroptera).