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

During the moulting and reproductive cycles, which coexist in adult females of the primitive insect Thermobia domestica , the corpora allata (CA) undergo periodical changes: their volumes and numbers of cells are lower at the beginning and at the end of each moulting cycle, and higher about the middle. However, the nucleo-cytoplasmic ratio does not undergo significant variations. An ultrastructural description of the CA cells is given for the first time in a lepismatid. The glandular cells, which are all similar, undergo 2 different stages: the so-called “clear cells” present at the beginning and the end of the moulting cycle, and the “dense cells” in the middle of the cycle. If there is no insemination at the beginning of each intermoulting period, the terminal oocytes are totally resorbed and most of the CA cells are in an intermediate stage between clear and dense cells. These data are discussed in relation to the probable variations in the physiological activity of the CA during normal adult cycles.

Modifications volumetriques et ultrastructurales des corpora allata du lepisme Thermobia domestica (Pacard) (Thysanura : Lepismatidae) au cours des cycles biologiques

The panoistic ovarioles of Lepismachilis targionii (Machilidae) possess external and internal sheaths. The external sheath occurs as a simple flat epithelium around the germarium; at the level of the vitellarium, the epithelium is replaced by a network of muscle fibres. The internal sheath constitutes the tunica propria, an acellular layer made up of superposed lamellae. The number of the lamellae varies along the ovariole; the maximum thickness of the tunica is reached in the anterior region of the vitellarium, where the lamellae are highly folded. Tracheolar cells and haemocytes are found at the side of the ovariole sheath. Some of the haemocytes, which apparently seem to be granulocytes, contain particular granules, provided with regular rows of microtubules. Cytological observations indicate that these multitubular granules de differentiate into vacuoles, whose fine granular contents discharge into the haemocoele by exocytosis. It seems that the granulocytes contribute to the formation of the thin basement lamina which surrounds the ovariole sheath; but they probably do not secrete the material of the tunica propria.

Structure de la Gaine Conjonctivo-Musculaire Entourant les Ovarioles de Lepismachilis Targionii (Grassi) (Thysanura: Machilidae). Role possible de granulocytes presents a son contact

In order to extend our knowledge of the neurohaemal organs in apterygote insects, a comparative description of the fine structure of these organs and of the aorta is given in 2 species: Thermobia domestica (Packard) (Thysanura : Lepismatidae) and Trigoniophthalmus alternatus (Silv.) (Microcoryphia : Machilidae), which are representative of the 2 now separated orders in the Thysanura (s.1.). In both species, the cephalic neurohaemal organs are formed by a pair of swellings of the aortic nerves, containing numerous axon terminals filled with neurosecretory (NS) granules, but only the NS axons of Thermobia are enveloped with glial cells. The NS products, which are not exactly similar in the 2 species, can be released into the aortic cavity. In addition, the lepismatids possess a pair of corpora cardiaca with intrinsic secretory cells, situated in the path of the cardiac nerves, close to the brain. In machilids, such endocrine organs do not exist, but a median organ—the infra-aortic corpus—also containing endocrine cells, is found in contact with the ventral aorta and connected, on each side, with the tritocerebral lobes. These observations on the neurohaemal systems agree with the concept that the machilids form a primitive group, distinctly separated from the lepismatids, which have many anatomical characteristics similar to those of lower pterygote insects.

Ultrastructure of the cephalic neurohaemal organs and of the corpora cardiaca in Thermobia domestica (packard) (Thysanura : Lepismatidae) and Trigoniophthalmus alternatus (silv.) (Microcoryphia : Machilidae)

Jacques Bitsch

Papers

Modifications volumetriques et ultrastructurales des corpora allata du lepisme Thermobia domestica (Pacard) (Thysanura : Lepismatidae) au cours des cycles biologiques

Structure de la Gaine Conjonctivo-Musculaire Entourant les Ovarioles de Lepismachilis Targionii (Grassi) (Thysanura: Machilidae). Role possible de granulocytes presents a son contact

Ultrastructure of the cephalic neurohaemal organs and of the corpora cardiaca in Thermobia domestica (packard) (Thysanura : Lepismatidae) and Trigoniophthalmus alternatus (silv.) (Microcoryphia : Machilidae)