No. 549] 



A CASE OF I'OLYMOh'PIIISM 



Ml 



As soon as I had discovered the fact that the humped 

 Asplanchna which I was studying was represented by a 

 saccate type which in many characters approached closely 

 to Asplanchna bright irelU, I began an extended search 

 for this latter species, in order to study closely the ques- 

 tion of relationship or non-relationship. At different 

 times, throughout a period of one year, I succeeded m 

 finding A. bright irrlli in five different ponds in my own 

 vicinity. The species tenants ponds of a different char- 

 acter from those in which the larger Asplanchna 

 nourishes, and is associated with a somewhat different 

 micro-fauna. In but one instance have I found the two 



blance of its occasional representatives to the more 

 numerous and likewise saccate individuals of A. bright 

 welli was so great as to almost prevent its detection. 

 Only my constant work with the larger species could have 

 sharpened my attention to the point of noticing any 

 especial lack of homogeneity in the material. Yet the 

 saccates of the larger species were regularly a little 

 longer and about one fourth broader than the adult A. 

 brightwelli. They differed also in a number of minor 

 constant characters. But none of these have hitherto 

 found place in any specific descriptions, with the excep- 

 tion of the difference in the trophi. The trophi of the 

 larger saccates agreed with the description and fignre 

 which I have given in everything save that they were a 

 little undersized. The trophi of A. bright nrlli agreed in 

 their general outline with the figure given for this specif 



ovalVontour. and mvariably lacked the large inner tooth, 

 just as Rousselet asserts that he has always found them 

 to do. Into the question of the form of their tips and 

 the presence or absence of the all but invisible lamellate 

 teeth I do not go. Such study as I have given them led 

 me to think that they were constructed in these respects 



