152 THE CRAYFISH 



and an exopodite which is fused with the epipodite so that it looks 

 like a continuation of it. What is the function of the fused exopodite 

 and epipodite? The first maxilla, the smallest of all the appendages, 

 consists of three parts, the endopodite and a bilobed protopodite. 

 Which is which ? Remove the right second maxilla and draw, orienting 

 as above. 



(h) Remove and make a similar figure of the right first maxilla. 



(i) The mandibles are now exposed. Against their posterior sur- 

 faces is a pair of lobes which are not true appendages. Each mandible 

 consists of a heavy basal portion on the median surface of which is a 

 cutting edge. This is shown by its development to be formed from 

 the protopodite and to be comparable to the more delicate median 

 outgrowths on the first and second maxillae. The three-jointed palp, 

 which protrudes from the heavy basal piece has its proximal joint 

 formed from the protopodite and the other two from the endopodite. 

 The exopodite is wanting in the adult. Where would it be if it were 

 present? Remove and draw the mandible of the right side, orienting 

 as above. 



(j) The antennae will show, when examined in place on the speci- 

 men, the typical exopodites, endopodites, and protopodites, and also 

 the openings of the green glands. Remove the right one of this pair, 

 orient, and draw. 



(k) The antennules are the only appendages which do not show 

 a true division into the three fundamental parts, although their two 

 terminal portions suggest the endopodite and exopodite. Remove one 

 and examine more carefully the region of the statocyst, or organ of 

 equilibrium. 



(1) Review the homologies indicated by the foregoing study. As 

 a matter of definition how would you distinguish serial homology from 

 the homology between the arms of a man and the wings of a bird. 



V. REGENERATION, REPRODUCTION, AND DEVELOPMENT 



Exercise 7. — Regeneration. 



(a) Crayfish are often found in nature with one or more great 

 claws or with walking legs missing or in process of regeneration. Ex- 

 amine such specimens if available. What is the relation of this re- 

 generation to the process of molting? Sudden detachment, or autot- 

 omy, of the great claw is a common reaction when the claw is seized 

 by an observer or by an enemy in nature. Try to demonstrate this 

 by holding one or both the claws of a living crayfish. What is the 

 nature of the so-called breaking joint? 



