ITS OUTER SKELETON. 



69 



Pleural elements are developed in the form of narrow 

 stigmatic plates, with the free edge directed backwards. These 

 lie between the terga and sterna, and defend the spiracle.* 



The modifications of the hindmost abdominal segments will 

 be more fully considered in connection with the reproductive 

 organs. 



<f 9 



Fig. 32. Under side of Abdomen of Male and Female Cockroach. X 4. 



The high number of abdominal segments found in the Cock- 

 roach (ten or eleven) is characteristic of the lower orders of 

 Insecta. It is never exceeded ; though in the more specialised 

 orders, such as Lepidoptera and Diptera, it may be reduced to 

 nine, eight, or even seven. The sessile abdomen of the Cock- 

 roach is primitive with respect to the pedunculate abdomen 

 found in such insects as Hymenoptera, where the constricted 

 and flexible waist stands in obvious relation to the operations 

 of stinging and boring, or to peculiar modes of oviposition. 

 The first abdominal segment, which is especially liable to dis- 

 location and alteration in Insects, occupies its theoretical 

 position in the Cockroach, though both tergum and sternum 



* Gerstaecker has found in the two first abdominal segments of Corydia carunculi- 

 gera (Blattarice) pleural appendages, which are hollow and capable of protrusion. 

 They have no relation to the stigmata, which are present in the same segments, and 

 their function is quite unknown. See Arch. f. Naturg., 1861, p. 107. 



