No. 548] A CASE OF POLYMORPHISM 



401 



the smaller saccates. It seems probable that the vigor 

 of the Asplanchna stock, and, I think, the period in the 

 reproductive cycle (number of generations since the rest- 

 ing egg), have much to do with the refusal or attack of 

 this oversized food organism. Be this as it may, how- 

 ever, the habit of eating the young Moinas, once started, 

 seems to rapidly become fixed in not only the individual, 

 but its progeny and the whole subsequent stock ; although, 

 weeks later, perhaps, this feeding reaction may again be 

 lost, and the last rotifers starve to death in the presence 

 of abundance of young Moinas. Such starving stocks 

 may be again revived, when almost perished, by the sup- 

 ply of a smaller food organism. 



Now the feeding upon this crustacean has, to all ap- 

 pearance, the same effect in bringing about the produc- 

 tion of the large campanulate type as has cannibalism. I 

 have not proven it with the same precision, but I have 

 observed the transformation of mass cultures from the 

 smaller to the larger type under circumstances that sug- 

 gested the all but certain conclusion that Mohia-ieednvj; 

 was the initial cause. I have also reared large numbers 

 of the campanulates, for weeks at a time, by using the 

 young Moinas as food. Under these circumstances the 

 humped rotifers all but disappear from the cultures. A 

 few always remain, because they are continually being 

 produced, in minor numbers, by the campanulate type. 

 But as very few of the humped young are able to acquire 

 the habit of Mo ma -feeding, they starve to death without 

 reproduction or fall victims to their mammoth progen- 

 itors. 



In one instance, and one instance only, I have followed 

 the transformation of the Asplanchna to its largest type, 

 through ilfoma-feeding, in nature. The case interested 

 me much, being very different from any other instance 

 that I have followed, and showing to an astonishing de- 

 gree the protean possibilities of the species. As usual, 

 the first appearance of the species was in this instance 

 by scattered individuals of the saccate form. Their food 



