A CRAYFISH OR A LOBSTER 39 
The reproductive system. The female genital organs. The posi- 
tion of the ovaries has already been observed. In the crayfish 
their forward portions are paired, while their hinder portions 
are fused and lie in the median line. In the lobster, however, 
no such fusion takes place, but the two ovaries are united by a 
bridge midway in their length. Find the paired oviducts which 
lead from the ovaries to the genital openings. Remove both 
ovaries and oviducts from the body and float them in water. 
Exercise 22. (a) Make a diagrammatic sketch of them. 
The male genital organs. The position of the testes has been 
already noted. In the crayfish they are similar in shape and 
position to the ovaries in the female animal, but are more 
slender; in the lobster they are a pair of long white tubes 
which extend forward as far as the stomach and back into the 
abdomen. Find the paired vasa deferentia, which are long con- 
voluted tubes connecting the testes with the external genital 
openings. Remove the vasa deferentia with the testes from 
the body and float them in a pan of water. 
Exercise 22. (6) Make a diagrammatic sketch of the male 
reproductive tract. 
Cut open a vas deferens and examine its contents under a 
high power of the microscope. Star-shaped spermatozoa will be 
seen. 
Exercise 22. (c) Draw a spermatozoan. 
The digestive tract consists of the mouth, esophagus, stomach, 
intestine, into which open the paired livers, and the rectum. Pass 
a probe through the mouth into the stomach and notice the 
dorso-ventral course of the esophagus, which joins the mouth 
with the stomach. The paired ducts which unite the two lobes 
of the liver with the intestine join that organ just back of 
the stomach. Find them. With scissors sever the esophagus 
