DEDIFFERENTIATION IN ECHINUS LARVAE. 2IQ 



their arms (similar to my Fig. i, b, or i, d) are able to regener- 

 ate them, while those which have dedifferentiated to a completely 

 spheroidal mass can probably redifferentiate to a pre-pluteus 

 (helmet-shaped) stage at least. Mr. Gray, however, proposes 

 to investigate the matter further, and I merely quote his pre- 

 liminary results in order to show that dedifferentiation does not 

 preclude recovery, at any rate to some degree. As is well known, 

 dedifferentiation in Clavellina and in Protozoa does not preclude 

 complete recovery (Driesch, '06; Lund, '17, etc.). 



The observations I have made, however, on forms dediffei- 

 entiated by KCN and HgCL (in which case dedifferentiation 

 appears to be slower than when caused by citrates) have not yet 

 shown recovery, though many specimens lived for weeks in sea- 

 water, and ingested food. From the present results, it would 

 seem as if the poison had robbed the organism of its capacity 

 for development, but not of its capacity for maintaining life. I 

 must emphasize that owing to lack of more ripe Echini, I was 

 unable to do more than carry out preliminary observations, and 

 that systematic experiments on the subject are in view. 



That being so, I will record my results in the briefest possible 

 manner. Most moderately-dedifferentiated forms (i.e., with cili- 

 ated band, but arms absent or vestigial) transferred to sea- water 

 from KCN remained alive and in approximately the same condition 

 for over 4 weeks. They kept on the bottom, and retained a slight 

 motility. In one culture the beginnings of recovery were noted 

 in the shape of increased motility and of a few larvae beginning 

 to swim freely once more, but after a few days they again re- 

 verted to their former condition. In all cultures a slight progres- 

 sive dedifferentiation was noted after i to 2 weeks, and towards 

 the end of the 4 weeks, a larger proportion of spheroidal forms 

 was found. 



On adding Nitschia to two cultures, it was found that diatoms 

 were ingested by many of the dedifferentiated larvae. These cul- 

 tures lived better than those without Nitschia. 



A number of these larvae were also placed, after 2 weeks, in a 

 jar with Nitschia and a stirring apparatus; but 3 weeks later none 

 could be discovered. 



The history of those transferred to sea-water from HgCL is 



