BLATTODEA. 67 



goes by the same name. The lamina subgenitalis is 

 the last visible ventral plate in both sexes. The 

 10th dorsal plate is called the lamina supra-analis, 

 and is different in shape in the two sexes. 



From beneath the edo-es of the 10th segment in both 



o o 



sexes spring the cerci, which vary in shape and are 

 usually jointed, the number of segments in Blafta 

 orientalis and Peri/planeta australaside being sixteen. 

 Seeing that these appendages are supplied with large 

 nerves, it would seem that they are not merely orna- 

 mental ; perhaps they serve as posterior antenna.* 

 They seem often to vary in development almost in 

 direct proportion to that of the alar organs, being to 

 all appearance absent in many wingless forms, though 

 search will reveal them as small plates. 



Besides the cerci the males in some s'pecies have, 

 projecting from the lamina subgenitalis, two styles. 

 These are absent from the adult females, though they 

 are present in the nymphs. Perhaps they are homo- 

 logues of the true legs, and, if so, constitute one more 

 point tending to show how old, as a family, the cock- 

 roaches are. The males of some species have glands 

 on the dorsal surface of the abdomen, towards the 

 apex, which may be " scent glands. There are ten 

 pairs of spiracles, eight being on the abdomen, and 

 two on the thorax between the bases of the legs. 



Occasionally a female may be noticed with a horny 

 purse-like capsule protruding from the hinder end of 

 her abdomen. This is the ootheca or egg- case (fig. 13). 

 It is formed inside the body of the female, and in B. 

 <>>-ientalis contains sixteen eggs in two rows of eight. 

 Till that number is complete the case is carried about, 

 and then, after a time some days maybe- -it is 

 deposited. In many cases the ootheca is wanting, and 

 it is possible that cockroaches of the past had it not, 

 for Brogniart credits some with an exserted ovipositor. 

 In some cases the ootheca is retained within the brood- 



* It seems that olfactory sense organs are considered to be borne by the 

 cerci, as well as by the antennse (Hauser, Forrel, etc.). 



