DIGESTIVE SYSTEM. 159 



season it will be found filled with an opaque 

 white seminal mass. 



Treat a small piece according to directions on p. 82 ; cover, 

 and examine it with low and high powers. 



iii. The spermatozoa are flattened spheroidal cells 

 from which project tangentially a number of 

 stiff immobile curved processes. 



b. In the female. 



i. The ovary is a saccular organ situated below and 

 at the sides of the pericardial sinus, and 

 extending some distance behind it. Like the 

 testis, it consists of two anterior lobes and a 

 posterior one. 



ii. The oviduct of each side is a short wide almost 

 straight tube, running from about the middle 

 of the length of the ovary, with which it is 

 continuous, to the external opening on the 

 coxopodite of appendage XL, the last thoracic 

 leg but two. 



C. The Digestive System. 



The alimentary canal of the crayfish is a tube running in a 

 nearly straight line from the mouth to the anus. Of this tube 

 the middle portion or mesenteron, which is very short, is alone 

 formed from the primitive alimentary tract of the embryo, 

 and the ' liver ' is an outgrowth of it. The stomodceum, or 

 anterior portion of the canal, and the protodoeum, or hind 

 portion, which together form almost the whole length of the 

 canal, are both formed by invagination of the external surface 

 of the body ; and both have a chitinous fining which is con- 

 tinuous, at the mouth and anus respectively, with the chitinous 

 external covering of the body. 



1. The digestive glands. 



a. The * liver ' is a large bilobed body, of a brown or 

 greenish colour, lying in the thorax at the sides 



