THE CRAYFISH lOI 



artery posteriorly to the telson and anteriorly to the sternal 

 artery. 



(4) The organs extending lengthwise under the heart 

 are the reproductive organs. In the female are found the 

 yelowish ovaries in which at certain seasons of the year 

 the spherical eggs may be seen. Note the position of the 

 masses and their relation to the other viscera. Examine 

 the tube leading from the ovaries to the surface at the 

 third thoracic leg. This is the oviduct. In the male the 

 reproductive organs are similar in shape to those of the 

 female though smaller in size. Study the color, position 

 and shape. The vas deferens is the tube leading to the 

 surface at the first thoracic segment. Follow it. 



(5) Carefully cut away the roof of the head. Find the 

 stomach with a thin wall in which is a hard framework. Re- 

 move the soft tissues from around it. Do you see the esoph- 

 agus, or gullet, extending from the mouth to the stomach? 



(6) The large reddish or brownish masses around the 

 posterior end of the stomach are the lobes of the liver. Pick 

 one to pieces and study its structure. 



(7) Observe the white muscles which extend forward 

 from the abdomen along the sides of the body cavity. 



(8) Beginning at the anterior end of the abdomen cut 

 through the tergum on each side down to the telson. Seize 

 this roof with the forceps and remove it, cutting the muscles 

 with the scissors if any adhere. The mass that you nov/ 

 see is the mass of abdominal muscles. 



(9) Running lengthwise in the middle is the intestine. 

 Follow it up to the stomach. Follow it down to the poster- 

 ior end, the anus, and observe any variations in size. Draw 

 the entire alimentary canal. 



