ABDOMEN AND ITS APPENDAGES. 



529 



St 



FIG. 437. Posterior end of body of a Beetle. 

 (Pterostichus $ ) (after Stein). 8, 9, Dorsal plates 

 8' &, ventral plates; St, Btigma ; A, anus; G, 

 genital opening. 



from one another by soft connecting membranes. They are com- 

 posed of simple dorsal and ventral plates, which are also connected 

 laterally by soft membranes. This structure of the abdomen, which 

 contains the respiratory and genital organs, permits of its being 

 dilated and contracted (respiratory movements, distension of the 

 ovary). Very often the posterior segments have a special struc- 

 ture, owing to the various 

 appendages which are con- 

 nected with the processes 

 of copulation and of depo- 

 sition of the eggs. The 

 anus is usually placed on 

 the last abdominal ring, 

 while the generative open- 

 ing which is separate from 

 the anal aperture opens 

 on the ventral surface of 

 the preceding segment (fig. 437). Terminal appendages, such as 

 jointed filaments, etc., are present on the anal segment. The ap- 

 pendices genitalcs, forming the genital armature, are, on the con- 

 trary, placed on the ventral 

 side around the genital open- 

 ing. Developed in the male 

 as valves and in the female 

 in the form of ovipositors, 

 gtings, etc., they arise from 

 the imaginal discs (growths 

 of the hypodermis), in the 

 Hymenoptera and Orthop- 

 tera on the eighth (first 

 pair) and ninth (second 

 pair) segments of the ab- 

 domen (fig. 438). The 

 ovipositors of the Diptera, 

 on the other hand, are to 

 be derived from the re- 

 tracted posterior segments. 

 Alimentary canal (figs. 

 439, 440). The mouth, 

 which is covered by the upper lip, usually leads into a narrow resopha- 

 gus, into the anterior portion of which, distinguished as the buccal 



34 



FIG. 438. a, Hind end of abdomen of a young 

 female Locusta with the protuberances of the 

 ovipositor and the anal styles ; C' and C"', the 

 internal and external protuberances of the penulti- 

 mate ; C"', the same of the antepenultimate seg- 

 ment, b, slightly older stage, c, Nympha ; A, anus 

 with anal styles (after Dewitz). 



