2IO EDMUND B. WILSON. 



obviously form a series, at one extreme of which the large chela, 

 after its removal, reappears and remains permanently of the 

 small type, with transformation of the small chela into one of 

 the large type (Alpheus) ; in the Brachyura the first process 

 occurs but not (as far as the observations show) the second ; 

 while in Homarus the large chela shows transitional characters 

 from a very early period. 



In the case of Alphcus it is a tempting conclusion that the initial 

 factor (Auslosung) that sets in motion the complex process of 

 differentiation of which either side is capable, is primarily only a 

 difference in the amount of material on the two sides. 



Mr. C. T. Brues has at my suggestion undertaken a study of 

 the internal changes and has determined the interesting and un- 

 expected fact that the nerves supplying the two chelae do not 

 differ perceptibly in size ; and they appear further not to differ in 

 the number of the component nerve-fibers or the size of the 

 ganglionic centers from which they proceed. As far as the 

 nervous system is concerned, therefore, the adult appears to retain 

 the bilateral symmetry of the larval form, the asymmetry arising 

 through hypertrophy in other tissues, Removal of the large 

 chela obviously reverses the asymmetry in respect to these tis- 

 sues, and must temporarily at least, lead to a functional nervous 

 difference on the two sides which may be accountable for the 

 release of development in the small chela. This is, however, 

 only a suggestion that must await further test. 



The interest of the general interpretation offered above, which 

 is essentially similar to the one suggested by Zeleny in the case 

 of Hydroides, seems to me to lie in the explanation that it offers, 

 of a regulative process of undoubtedly high utility to the animal, 

 that is in the main effected by the same factors as those operative 

 in the normal development ; and it seems not unlikely that many 

 regulative processes in regeneration may be capable of a like 



interpretation. 



ZOOLOGICAL LABORATORY, COLUMBIA UNIVERSITY, 

 January 15, 1903. 



