ZOOLOGY I)I}?ECTIONS 



to the annulus veniraHs of the female. Make a drawing of the 

 reproductive organs of your specimen. 



See demonstration specimen of female crayfish carrying 

 eggs on the swimmerets. The eggs, after fertilization, become 

 attached to the swimmerets where they undergo development. 



Digestive System 



1. The digestive tube extends from the mouth to the anus. 

 The liver (or more correctly the hepato-pancrcas) is a large 

 bilobed organ which lies below the ovaries or testes. These lobes 

 lie along either side of the digestive tube. Each lobe connects 

 by a duct with the main digestive tube. 



2. Turn the animal over and on the ventral side examine 

 the mouth between the jaw^s. Insert a probe into the mouth. 



3. A short wide passage, the esophagus, leads upward from 

 the mouth. 



4. The esophagus leads to a large dilated portion of the 

 canal, the stomach. This occupies the main portion of the head 

 region. The larger cardiac chamber lies in front and the smaller 

 pyloric chamber lies behind. The two are separated by a nar- 

 row constriction. 



5. The region of the mouth, esophagus, and the stomach 

 are lined with chitin and are formed by an infolding of the outer 

 skin of the animal as it develops. These parts are collectively 

 known as the fore-gut. 



6. Posterior to the fore-gut is the mesenteron or mid- 

 gut. This part lacks the chitinous lining and receives the ducts 

 from the liver. 



7. The hind-gut, which leads to the anus is the part of 

 the digestive tube behind the mesenteron. Trace its course. 

 This develops from an infolding of the outer surface and is 

 lined with chitin. 



