118 



LIBBIE H. HYMAN 



The axial gradient of other naids is similar in all respects to 

 that of Dero limosa, and the changes connected with zooid 

 formation are also the same. I have examined Stylaria lacustris 

 in some detail with regard to the gradient, and Dero furcata, and 

 Nais eUnguis less thoroughly, and these forms agree completely 

 with Dero limosa. I have also performed some disintegration 

 experiments with the marine syllid, Autolytus cornutus, which 

 also reproduces asexually, and whose gradient is quite like that 



Fig. 12 Graph of the axial gradient of Dero limosa with a well-developed 

 zooid, showing the two independent gradients. 



of the naids. The polychaetes, are however, unfavorable for 

 this kind of experiment because they do not disintegrate readily. 

 The gradient of Chaetogaster diaphanus, however, is unlike that 

 of other naids, and is so peculiar that it would be profitless to 

 describe it. The very young zooids of Chaetogaster have, never- 

 theless, the primary gradient, but as soon as morphological differ- 

 entiation begins in the zooids, the primary gradient is replaced 

 by the adult gradient, whose chief peculiarity is that the head is 

 least susceptible to cyanide, while a small region at the posterior 



