A CASE OF POLYMORPLISM IN ASPLANCHNA, 

 SIMULATING MUTATION. II 



PROFESSOR J. H. POWERS, 



I may next state some further observations which I 

 was able to verify again and again in regard to the trans- 

 ition of one form of the species to another. As I have 

 said, forms intermediate between the saccate and the 

 humped, between the humped and the campanulate, and 

 even between the saccate and the campanulate, occur. 

 This statement applies to external body form, and to 

 some extent to the nephridia and other internal organs, 

 with the exception, however, so far as I have yet observed, 

 of the size of the contractile bladder. This latter seems 

 "to have its large size only in the small saccate type, and 

 I have observed no indications of gradual transitions to 

 the form possessed by the larger rotifers. More sig- 

 nificant, however, is the case of the trophi. I have ex- 

 amined these in a great many individuals that in body 

 form were more or less intermediate between the dif- 

 ferent types ; but in nearly every instance the variations 

 of this organ seem to be abrupt and discontinuous; the 

 trophi are either of one type or the other. The only 

 instances found that in any sense transgress this state- 

 ment were the trophi of a few saccates produced as the 

 result of the slow degeneration of the larger form, in the 

 culture which I have before mentioned. These animals 

 showed trophi that had plainly lost a number of the more 

 delicate characters which I had otherwise found universal 

 through such a wide range of material, and, simultane- 

 ously with this, they had become in a degree transitional 

 between the two types ; the angle of the inner tooth and 

 a slight crossing of the tips plainly related them to the 

 cannibalistic type, while in size and general form they 



