Crustacea. 43 



4. Under the heart, and projecting in front of it, are the repro- 

 ductive organs : in the female, the ovary, in which the spherical 

 eggs may be distinguished ; in the male, the whitish spermary oc- 

 cupies a corresponding position. The ovary sends downward on 

 each side a tube, the oviduct, or egg tube, to the first segment of 

 the third thoracic leg, where it opens externally. The spermary 

 has a much longer, coiled white tube, which opens on the first 

 segment of the hindmost thoracic leg. 



5. Carefully cut away the roof of the head. The space within 

 the head is almost completely occupied by the stomach, a round- 

 ish sac, with a thin wall, in which is a hard framework. Gently 

 scrape away the soft tissues around the stomach, and examine it 

 closely. Observe the narrow gullet or esophagus leading from the 

 mouth to the stomach. 



6. Along the sides of the posterior end of the stomach and the 

 anterior end of the intestine lie the large digestive glands. They 

 are yellow or greenish in fresh, reddish in alcoholic, specimens. 

 Pick one of these masses to pieces to learn its structure. Find 

 the duct leading from each gland into the intestine. 



7. Observe the white muscles which extend forward from the 

 abdomen along each side of the body cavity. 



8. Beginning at the front end of the abdomen, close to each 

 side, cut with scissors through the roof of the abdomen to the 

 telson. Seizing the forepart of this roof with the forceps, care- 

 fully lift it and turn it backward. A thir layer of white muscle 

 may adhere to it, or may remain connected with the organs in the 

 abdomen. This is made up of the muscles that straighten (ex- 

 tend) the abdomen. Pick them away carefully with the forceps. 



9. Running lengthwise, in the middle line, is the intestine, a 

 thin-walled tube, often of a dark color from its contents. Trace 

 it back to the anus and forward to the stomach. Carefully re- 

 move the intestine. 



10. A large mass of muscle remains. This is composed of the 

 muscles that bend (flex) the abdomen. How do these flexor 

 and extensor muscles compare in size? Why the difference? 



