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. (b) 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, oesophagus, 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 oesophagus, 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 oesophagus 



