Rate of Regeneration in Cassiopea xamachana. 85 



cases in series A, he will find the average period before molting to be 9743 

 days, while for the 13 individnals of series B it is only 60.77 fl^VS- If now 

 the average molting period of series A be multiplied by its specific rate of 

 regeneration, we have 9743X0.0049 = 0.4774, and a similar calculation 

 for series B gives 60.77X0.008 = 0.4861. The two products differ but 

 slightly. Thus the average specific rates of regeneration for the two series 

 are to one another as the average times between the operation and the first 

 molts. The average line of Zeleny's table 7 gives a similar result (0.42=: 

 0.633), b"*^ not so close as the above, where the two series have almost the 

 same number of individuals, 13 and 14; in Zeleny's table 7 series A contains 

 14 and B 20 individuals. The only legitimate conclusion to be drawn from 

 such figures seems to be that Caiiibariis regenerates a given amount (the 

 specific amount of regeneration") and stops until a molt occurs; if the 

 molt comes early, then the animal has an opportunity to continue its re- 

 generation ; and so it may be said that a crayfish which molts oftener will 

 regenerate a limb .sooner than one molting less often. Thus if greater in- 

 jury causes the crayfish to molt more promptly, they grow a limb sooner 

 merely on account of having more opportunity to grow, as the result of 

 frequent molts, but whether the specific rate of regeneration is more in those 

 with the greater degree of injury is not definitely shown. 



Zeleny states : " The more rapid regeneration of the limbs may be the 

 cause of the acceleration of the molting, or the opposite may be the case, 

 or finally the two phenomena may be coordinate and only indirectly re- 

 lated." In the crayfish it seems that the greater injury is accompanied 

 by more rapid molts, but I see no proof that the latter response results 

 from a more rapid regeneration. It may be due to the regeneration taking 

 place from a greater area." 



Of special interest in this connection are the results of Emmel ( 1907 I 

 on the lobster. Only an abstract of Dr. Emmel's paper has yet been pub- 

 lished. He has written me. liowever, that the specific amount of regenera- 

 tion at the time of the first molt was fairly constant, and this is the im- 

 portant point for comparison with Zeleny's results. Emmel found that 

 those individuals with the greater degree of injury molted slower, while 

 those less injured molted faster. The response is opposite to that of the 

 crayfish. The significant point is his conclusion that the rate of regenera- 

 tion was slower in the more injured series and faster in those less injured — 

 again an opposite conclusion from that of Zeleny. 



If Emmel's observations that the lobsters most injtired molt slower 

 than those less injured is correct, then his second conclusion of slower re- 

 generation from those most injured is clear. In the lobster, as in the 

 crayfish, the regenerating bud grows as long as possible and then is pre- 



' Emmel (1906) has shown that it is the process of regeneration itself which affects 

 the rate of mohing in the lobster. 



