THE CRAWFISH. 121 



(2) Organs of Reproduction. The reproductive organs 

 will be found just beneath the floor of the pericardial 

 sinus, whitish in the male, and with a pair of very long 

 convoluted tubes or ducts (one on each side), yellowish 

 (sometimes dark colored from the presence of eggs), in 

 the female, and with a pair of short, descending ducts. 



(3) Organs of Digestion. Study next the organs of 

 digestion, the alimentary canal and its appendages. Dis- 

 sect away all the organs that cover it. In doing this-, 

 observe in the abdomen a thin layer of muscle above the 

 straight intestine, and a thick layer below it. The upper 

 muscle extends to the abdomen, and the lower flexes it. 

 What reason is there for the much greater size of the 

 flexing muscle ? Make a shallow cut along the median 

 line of this lower muscle, and remove the upper half of 

 it. It will separate easily, if taken in a single long roll. 



A pair of big forceps, three pairs of maxillipeds, two 

 pairs of maxillae, and one pair of mandibles, have already 

 been found to be the external agents for the communica- 

 tion of food. The food passes from the mouth directly 

 upward through a short esophagus, into a large, bag-like 

 stomach, which nearly fills the head cavity, and extends 

 backward a little way into the thorax. It is divided into 

 two chambers by a constriction. On either side of its 

 posterior end are a pair of large yellow or brown glands, 

 which are accessory organs of digestion, called liver. 

 Find the ducts by which they pour their secretions into 

 the alimentary canal. Posterior to these is the straight 

 intestine. 



The comminution of the food is continued in the 

 stomach, the internal surface of which is armed with 

 hard teeth and ossicles, which make it a grinding organ. 

 Cut it open, and find these hard parts. The food passing 

 out from the stomach is mixed with secretions from the 

 liver, and is digested. It then passes through the walls 



