Rate of Regeneration in Cassiopea xamachana. 83 



in which all of the mouth-arms are, Hkevvise. ahnost similar in size and form 

 and regenerate by a process of continuous growth, that wide variations 

 are presented in the rate of regeneration of the several arms. The 

 series with a few removed arms may regenerate each arm as rapidly as do 

 those with a greater number of removed arms. An individual with several 

 arms cut away often shows as great variation in the regenerating rates 

 of the different arms as is found on comparing the average rates of indi- 

 viduals with few and many arms removed. Here it may be emphasized 

 that the variation in regeneration rates of the several arms of one and the 

 same individual (a variation shown to exist only slightly in most of Zeleny's 

 tables, but which is very striking in some of mine) is an index to the 

 dangers which arise when one compares the average rates of regeneration 

 found in several different individuals. Miss King (1898) also states in her 

 study of regeneration in Asterias that " the rate of growth of the new arms 

 is ordinarily unequal when a disk regenerates two or more at the same time." 

 Zeleny has studied three forms of decapod Crustacea — Gelasimns, Alphcus, 

 and Cambarus, the crayfish. He realized that so few individuals of Gela- 

 siinns and Alphcus were available for final comparison that it was unsafe 

 to draw general conclusions. In these two forms the chelae are of unequal 

 size and in Alpheus they undergo a reversal upon removal of the larger 

 one. (See Prizibram, 1901, and Wilson, 1903.) Zeleny cites such facts as 

 introducing complications in this study. The crayfish, Cambarus, has 

 the two chelae of equal size and for other reasons also is better suited to 

 regeneration experiments. After a careful study of jy individuals, 61 of 

 which were available for the final comparison, Zeleny concludes : 



That in the series with the greater degree of injury each chela regenerates more 

 rapidly than the single removed chela of the series with the lesser degree of injury. 

 Likewise [and this is the point that I shall attempt to show the importance of in 

 interpreting Zeleny's experiments] the members of the series with the greater injury 

 molt more rapidly than those of the series with the lesser injury. 



This work on the Crustacea seems to me to be open to criticism. Such 

 animals must molt before the regenerating bud is observed. The time 

 elapsing between the operation and the first molt varied from 27 to 181 

 days, and according to Zeleny, " the amount of regeneration of the right 

 chela at the end of the first molt is the same, no matter what the degree 

 of injury inay be." Further, " The specific ainount of regeneration at 

 the end of the first molt after the operation is a constant which is not 

 affected by the time of the molt, the size of the animal, or the degree of 

 other injuries to the individual." It seems almost inconceivable that one 

 animal should thus require nearly seven tiines as long to regenerate a bud 

 of a given length as was necessary for another to grow a similar bud. 



Zeleny now takes this "constant" (specific amount of regeneration at 

 the end of the first molt) and divides it by the number of days between 



