no 



LIBBIE H. HYMAN 



posterior end begins to disintegrate, and this disintegration pro- 

 ceeds anteriorly. The two waves of disintegration meet some- 

 where about the middle of the zooid. The interpretation of this 

 sort of gradient is simple. Annelids grow characteristically 

 by the formation of new segments in front of the anal segment; 





l^ 





4::h 



Mm 



m 

 1 



Fig. 6 Two stages in the disintegration of an Aeolosoma with a zooid, show 

 ing the secondary posterior rise in the principal zooid. 



the new segments thus formed would be expected to have a high 

 rate of metabolism, and therefore an increased susceptibility to 

 cyanide. As soon as the Aeolosoma individual has formed a 

 posterior zooid, it begins to grow in this fashion at its new 

 posterior end, and this growing region shows increased suscepti- 

 bility to cyanide (fig. 6). In fact, this process may go to such an 



