EMBRYOLOGY OF ONISCUS. 287 
shaped, widest behind, extending a little behind the middle 
of the body. ‘The intestine is about one half as wide as 
the stomach. Oertain Isopods possess segmental organs. 
Fig, 251.—Dissection of Serolis to show the nervous system.—Dissected and drawn 
by J. S. Kingsley. 
There is no cecal enlargement, and no “urinary” tubes. 
The sexes are distinct. The young are hatched in the form 
of the adult, there being no metamorphosis. 
The development of the pill-bug, Oniscus murarius, is 
probably typical of that of most Tetradecapods and Deca- 
Fig. 252.—Transverse section of Serolis. t, ¢, tergum ;'s, s, sternum ;_em, epime- 
Tum ; ¢é, episternum, at insertion of the legs.—Prepared and drawn by J. S. gee 
ley. 
pods (Bobretzky). The first change after fertilization is the 
origin of the formative or primitive blastodermic cells at one 
