Hio

cording to Snodgrass (1957), the evidence from embryonic and postembryonic development does not support assumption (2) but indicates that the genitalia arose primitively on the tenth abdominal segment.

5.2.2. Other Appendages

Cerci. Paired cerci occur in Diplura, Microcoryphia, Zygentoma, Ephemeroptera, Zygoptera (a suborder of the Odonata), Plecoptera, the orthopteroids and blattoids, and Mecoptera. It is generally agreed that the cerci (Figure 3.31) are true appendages of the 11th segment, although frequently all traces of the latter have disappeared. Typically, they are elongate multisegmented structures that function as sense organs. They may, however, be considerably modified. In nearly all Dermaptera the cerci form unjointed forceps. The cerci of nymphs of Zygoptera are modified to form the lateral caudal lamellae (Figure 6.11C). The latter, along with the median caudal lamella (developed from the epiproct), are accessory respiratory structures. In adult male Zygoptera the cerci form claspers for grasping the female during copulation. In most male Embioptera the basal segment of the left cercus forms a hook with which the insect can clasp his mate.

Styli and Eversible Vesicles. Styli occur on most abdominal segments of Microcoryphia, Zygentoma, and Diplura, and on the ninth sternum of some male orthopteroids. In some bristletails the styli are articulated with a distinct coxal plate (Figure 3.34), but generally the original coxal segment is fused with the sternum. In bristletails, at least, the styli serve to raise the abdomen off the ground during locomotion.

Eversible vesicles (Figure 3.34) are short cylindrical structures found on some pregen-ital segments of apterygotes. They are closely associated with the styli when present, but their homology is unclear. They are believed to have the ability to take up water from the environment.

FIGURE 3.34. Stylus and eversible vesicle of a thysanu-ran. Part of the wall of the plate has been removed to show the musculature. [From R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company.]

suprapedal lobe —

flexible integument planta

FIGURE 3.35. Secondary segmental appendages. (A) Proleg of a caterpillar; and (B) gill of a mayfly larva. [From R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company.]

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Beekeeping for Beginners

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