THE CRAYFISH 113 



Of what advantage is this form? To what are the gills 

 fastened? How does the water get to the gills? Why are 

 they under the carapace? 



2. Circulatory System. Carefully remove the carapace 

 from the dorsal side of the body. The heart will be found 

 in the posterior portion of the cephalothorax, as a delicate 

 shield-shaped body. Notice any vessels which extend out 

 from the heart and examine an injected specimen, if one is 

 available. Note the small openings in the heart, these are 

 valves. In what direction do they permit the blood to flow? 

 Trace all the bloodvessels which can be found. 



3. Reproductive System. The ovaries are granular bodies 

 of considerable size located in the dorsal part of the thorax 

 and abdomen. Note the shape and extent of the organ 

 and trace the ducts to the openings already noted. The 

 testes are in a similar position but are smaller and are of a 

 whitish color; the sperm ducts are somewhat coiled and 

 longer than the oviducts. 



4. Digestive System. Remove the gills from one side of 

 the body and cut away the body wall of the same side. This 

 will expose the greenish liver and the other digestive organs. 

 Remove .the lobe of liver on this side and expose the stomach 

 and intestine. 



In the extreme anterior part of the body cavity will be 

 found the large stomach composed of two parts, from which 

 the intestine leads backward to the anus. Between the 

 mouth and the stomach there is a short esophagus. Trace 

 the digestive tube from the mouth to the anus, observing 

 the shape and the size of the parts and their exact position. 

 Do the large digestive glands, or livers, open into the intestine 

 or the stomach? 



Draw the animal from the side as opened and show all 

 the organs that are exposed or that can be seen by dissection. 

 8 



