30 PHYLUM ARTHROPODA 



fish their forward portions are paired, and their hinder portions 

 are fused and He in the median Hne. 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 22y 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 posi- 

 tion 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 sperm ducts, which are long, convoluted tubes con- 

 necting the testes with the external genital openings. Remove 

 the sperm ducts with the testes from the body and float them in 

 a pan of water. 



Exercise 22 ^ b. Make a diagrammatic sketch of the male reproduc- 

 tive tract. 



Cut open a sperm duct and examine its contents under a high 

 power of the microscope. Star-shaped spermatozoa will be seen ; 

 if, however, the specimen has not been well preserved they will no 

 longer be present. 



Exercise 22y c. Draw a spermatozoon, if present. 



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 just ventral to the 

 stomach, taking care not to injure the brain, which Hes in front 

 of the stomach, or the two slender nerve connectives, which he on 

 either side of the oesophagus. Sever the rectum near the anus. 

 Remove the entire digestive tract from the body and place it in a 



