EMBRYOLOGY OF ON ISO US. 



307 



shaped, widest behind, extending a little behind the middle 

 of the body. The intestine is about one half as wide as the 

 stomach. 



Fig. 256. Dissection of Serolis to show the nervous system. Dissected and drawn 

 by J. S. Kingsley. 



There is no ccecal 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- 



Fi-. 257. Transverse section of Serolis. t, t, tergum ; *, s. sternum ; em, epime- 

 rum 1 ; es, episternum, at insertion of the legs. Prepared and drawn by J. S. Kings- 

 ley. 



pods (Bobretzky). The first change after fertilization is the 

 origin of the formative or primitive blastodermic cells at one 



