164 



GENERAL ZOOLOGY 



places. The flattened condition of the body reminds one of 

 the cockroach, which shows the same adjustment of the 



form of the body to the necessities of life. 



The species represented (Fig. 89) belongs 



to the genus Onis'cus. 



The body has twenty somites, as have the 



crayfish and all the forms described so far in 



this chapter. A pair of short, jointed anten- 

 nae and a pair 



of compound 



eyes without 



stalks, that 



is, sessile eyes 



(Lat. sedere, 



"sit"), are 

 the most noticeable organs of 

 the head. They have a sec- 

 ond pair of antennae, which 

 are rudimentary. The mouth 

 parts are small and adapted to 

 feeding on plant food. The 

 breathing organs are 

 y gills, protected by 



Fig. 89. Sow bug. 



(x3) 





\ 



y 





>v:. 



• " 



*f '10^ 



-ST*" 



flat, plate-like struc- 



FiG. 90. Caprella. (x 2) 



tures on the under surface of the abdomen. The female 

 bears a brood pouch on the under surface of the body, 

 in which the eggs are carried and the young develop. 



