No. 548] A CASE OF POLYMORPHISM 



457 



become numerous, I find this giant type invariably pres- 

 ent. The original collection which I studied was about 

 typical in this respect. I have not ascertained the exact 

 proportion which the campanulates bear to the humped 

 form in any given case, for experiment shows that it is 

 capable of variation within wide limits ; but I think that 

 in nature they would rarely equal one to one hundred. 5 



What was the relation of these two types? Weeks of 

 all but continuous work were necessary to decipher it. 

 The fact that the two types were so frequently associated 

 indicated probable connection, but did not demonstrate 

 it; the fact that the campanulate always appeared only 

 long after the development of the humped form was again 

 suspicious, but proved nothing. Isolation cultures of the 

 campanulates soon showed, as my mounted material had 

 done, that they regularly produced not only their own 

 type, but a considerable proportion of the humped type as 

 well. But the reverse process is at least so rare that I 

 have been as unable to find it among my living material, as 

 I was among that which I had mounted. Scores of isola- 

 tion cultures, begun with few or single individuals, fed 

 on diverse types of food, and nearly all very successful, 

 remained negative in result, with the exception of one 

 of my very first attempts. I was trying out the rotifer, 

 Bydatina, as a possible food for the humped Asplanchna, 

 and placed half a dozen of the ordinary type in a watch- 

 glass with many of the smaller rotifers. Soon, among 

 the young produced, there appeared one that rapidly 

 developed into the giant type ; but subsequent trials, car- 

 ried on as long as this special food supply lasted, were 

 negative in results. 



Over against these failures, however, a large number 

 of my mass cultures yielded at once all hut conclusive 

 evidence that the larger type was somehow derived from 

 the smaller. These cultures were started as follows: 



