A prerequisite for metamorphic differentiation between juveniles and adults is therefore the inhibition of some normal inheritance processes. In addition, the different specializations of young people and adults can be mutually beneficial and therefore beneficial to the individual as a whole.
8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 122 though it is derived from an early stage of ontogeny, it is specifically
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 9
METAMORPHOSIS AND CLASSIFICATION
The insects classified as hemimetabolous are the Plecoptera, the Ephemeroptera, the Odonata and some of the Homoptera. In the Coccidae the wings of the male do not appear externally until the third or fourth molt, and in Aleyrodidae they do not appear externally until the last molt.
HORMONES AND METAMORPHOSIS
Variations in the relative position and connections of the corpora allata and cardiaca, and. The action of the corpus-allatum hormone is better known than that of the other endocrine organs.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 21
APTERYGOTA
That the stylets are coxal appendages and not limb remains is shown by their occurrence on the coxae of the middle and hind legs (B,5>y). Both styles and vesicles also occur among the other groups of apterygote insects, and among the pterygotes, styli are present on the ninth abdominal segment of the adult male in the cockroaches, man-.
PLECOPTERA
Similar tapering branchial processes are present on the sides of the first six segments of the abdomen in the genus Eusthenia, as illustrated by Tillyard (1926) in E. A group of long tubular processes arising in the anterior end of the rectum he considers as "blood gills" because they do not contain a trachea.
EPHEMEROPTERA
Just as the thysanuran stylets only appear after the first molt, so the gills of the mayfly larva are absent in the first stage. Gills of the simplest form are slender processes penetrated by tracheae, others are surrounded with long filaments, some are lamelliform, and most of them are branched.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 31 In various lesser ways the mayfly larva may be characterized by
ODONATA
While undoubtedly the larval labium is specialized in comparison with the adult labium, the labium of the embryo develops directly into that of the larva, and at metamorphosis the adult labium develops in the larval organ. 9 INSECT METAMORPHOSIS — SNODGRASS 35At an early stage of labial transformation in Anax Junius.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 35 At an early stage of the labial transformation in Anax Junius the
HEMIPTERA
The tarsus of the first instar (B) is reduced in later stages to a small scratch on the inner surface of the tibia (C, Tar), but it is completely restored in their natural nymph (D). In the transformation to the adult, the special features of the nymph leg are many. As described by Weber in Trialeyrodes vaporrariorum, the body of the young insect in the fourth instar becomes deeper than that of the previous instars.
In the first stage of metamorphosis, known as propupa, the male winged species begins to take on the form of an adult.
THYSANOPTERA
The metamorphosis of the muscular system, as given by Makel, is based on a detailed comparative examination of the muscles of the larva, pupa, and adult. However, one may wonder whether the coccid pupa is comparable to the pupa of the higher holometabolous insects. In the pupal stage, the antennae become longer, their segmentation becomes clearer, the shape of the head approaches that of the imago, the compound eyes become larger, the eyecups appear and the sexes are now distinguishable.
9 INSECT METAMORPHOSIS — SNODGRAS 47fosis in the latter part of the second larval stage the regenerative.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 47 phosis in the last part of the second larval stage the regenerative
OLIGONEOPTERA, OR TYPICAL ENDOPTERYGOTA
NEUROPTERA TO HYMENOPTERA
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 49 The endopterous condition of the larva and the substitution of
In the simplest type of wing development in modern endopterygote insects, as shown by Tower (1903) in some Coleoptera, the wing is first formed in the early pupa under the cuticle of the last larval stage and is therefore exposed to the pupa only at molt. In the first phase, wing growth was presumably suppressed until the end of the juvenile period; in the second stage, the wing embryos developed again in the early larval stage, but now sank into the epidermis below the cuticle, thus still maintaining "wingless". Typical larvae are simple single eyes, usually only a few in a group on each side of the head.
In the Culicidae and related Diptera it has been shown by Constantineanu (1930) that the compound eyes begin their development in an early stage of the larva.
52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 122 If we assume that the primary endopterygote larva was a modified
LARVAL HETEROMORPHOSIS
Heteromorphosis of the larva, commonly called hypermetamorphosis, occurs frequently among predaceous and parasitic species of insects, examples being known in Neuroptera, Coleoptera, Strepsiptera, Lepidoptera, Hymenoptera and Diptera. Two categories of heteromorphosis in parasitic larvae must be distinguished as the adult female lays her eggs in the open, or on or within the body or egg of the prospective host of the larva. However, after entering the nest or body of the host, the planidium changes into a second-stage larva of greatly simplified form and structure adapted to a sedentary life of parasitism.
During later instars, however, the simple larva adopts a shape more typical of the usual larva of its species.
PARASITES WITH A PLANIDIAL STAGE
The conversions of species of the American Epicauta are well known from the early works of Riley (1876) and later papers by Ingram and Douglas (1932) and Horsfall (1941). The female of Tricrania deposits her eggs under small objects lying on the ground near the nesting sites of the bees. Wadsworth (1915) gives a good account of the life history and larval stages of Aleochara bilineata, an aparasite of the cabbage.
The newly hatched larva is an active thysanuriform planidium that must seek the cabbage fly's puparium in the soil.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 67
The ovary is connected to the body cavity of the female by several funnel-shaped tubes. The young larvae that hatch from the eggs escape from the female's body through the ventral funnels into the brood egg. After hatching, the larva stands upright with the help of an attachment structure at the end of its abdomen, but it is.
The planidium (Fig. 13 B) enters the caterpillar's body through the skin and searches for the larva of a primary parasite, including both dipterous and hymenopterous species.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 75 The larval history of Schisaspidia tenuicornis shows how complex
PARASITES WITHOUT A PLANIDIAL STAGE
The caudal diverticula in the first stage have been elongated into a pair of tails nearly half the length of the body, and fine tracheal branches later penetrate their open basal parts. In the third stage, the body retains the general shape and structure of the second stage, but the tails have greatly increased in length and are one and a half times or more the length of the body. In the second stage, the Limnerium larva assumes a form of structure with a small head and 12 body segments, with the tail of the first stage being much shortened.
This head-like part of the larva has been shown by Marchal (1906) to be a cephalothorax bearing the antennae, the mouth.
NO. 9 INSECT METAMORPHOSIS SNODGRASS 79
In the first instar Hadronotus larva (Fig. 15 J) we again see an example of early specialization in shape, accompanied by delays in the development of organs not immediately needed. It is now nourished, like the eggs, by the secretion of the ovaries that ends up in the brood pouch. The so-called larva could be considered a second embryo, but it is clearly an adaptive form completely different from any other early stage in the development of common arachnids.
Whatever form the early larva may assume, however, it ultimately falls to the larva to return to its parent form, and.
XL THE PUPAL TRANSFORMATION
He noted that they are present in the epidermis during Rhodnius slides, and in greatest numbers where nuclei seem to be formed in excess of the need for new cells. Again, in the chrysomelid Galeritcclla, Poyarkoff (1910) finds little evidence of destruction of larval cells in the transformation of the epidermis from larva to pupa. On the other hand, in Hymenoptera and Diptera there may be a complete renewal of the epidermis from the imaginal discs of the larva.
As the new epithelium spreads from the generation centers, the old cells of the larval epidermis move outward.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 85
Because the stomodaeum and proctodaeum are of ectodermal origin, their changes in pupal metamorphosis are similar to those of the epidermis. The anterior ring serves only for the extension of the stomodaeum and the formation of the. The posterior ring is a narrow circle of cells in the intestinal wall just behind the bases of the Malpighian tubules.
The imaginal tubes then form as bud-like outgrowths from the extreme anterior end of the proctodaeum.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 95 go into a degenerative state to such an extent that they appear to be
Oenocytes.- Oenocytes are specialized ectodermal cells developed from the epidermis near the spiracles, mainly in the abdomen. Imaginal oenocytes develop independently of the abdominal epidermis near the spiracles, but in the image they are mostly scattered among fat body cells. The presence of histoblastic centers of regeneration in the tracheal system, as in other parts of the ectoderm.
Just before this, granular degeneration of the cells of the heart and pericardium occurs.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS IO3
Oertel does not discuss the genesis of free myoblasts, but says that "myoblasts are generally believed to be of mesodermal origin." In the case of regenerating abdominal muscles, he notes that the fibers are in some cases com-. According to Perez (1912), the larval muscles of Polistes wasps have two sets of nuclei, large larval nuclei in the body of the muscle and small embryonic nuclei. Blaustein's (1935) description of muscle transformation in the lepidopteron Ephestia kuhniella is not explicit as to the origin of the myoblasts, but this author states that they are future muscles.
The dorsal longitudinal muscles of the metathorax of the larva during degeneration lose their cross and sar- striation.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS IO5 In the higher Diptera there appears to be no doubt that the imaginal
MUSCLE ATTACHMENTS AND THE NATURE OF THE PUPA The somatic muscles of arthropods for mechanical reasons are
The nature of tonofibrillae and the mode of their formation have been debated for half a century and continue to be so. The pupal molt is the insect's solution to the problem of attaching new or reconstructed muscles. Williams (1952) has shown that the same hormone system, namely that of the brain and the mammary glands, regulates both the pupation of the larva and the adult development of the pupa.
More likely, the pupa was a secondary, independently evolved moult in the ancestors of the present holometabolic insects, rather than a.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS III
Development and metamorphosis of the midgut epithelium of Acanthoscelid.es obtectus (Say) (Coleoptera).
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 113
On the development of the midgut in the larval stages of Vanessa urticae (Lepidoptera). I039- On the African Streblidae (Diptera Acalypterae) including the morphology of the genus Ascodipteron Adens., and a description of a new species. On the Abdominal Appendages of Larvae of Trichoptera, Neuroptera, and Lepidoptera, and the Origin of Jointed Limbs.
On the larval characters and habits of the blister beetles belonging to the genera Macro Basis Lee.. and Epicaiita Fabr., with remarks on other species of the family Meloidae.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS 121
Remarques prelinaires sur l'alimentation, les organes chelicierens, le biberon et la tetinede l'embryon du scorpion: Ischnurus ochro-pits C. 1953a. Cocoon construction by the silkworm Cecropia I. The role of the external environment. On the life history of Alcochara bilincata Gryll., a staphylinid parasite of Chortophila brassicae Bouche.
NO. 9 INSECT METAMORPHOSIS — SNODGRASS I23
