No. 548] A CASE OF POLYMORPHISM 



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course I neither accepted at once the suggestion nor the 

 apparent facts before me. Mutation, although among 

 things proven, is among the things proven to be rare, and 

 is therefore to be accepted in any given case only after 

 fullest verification. Moreover, facts themselves are fre- 

 quently deceiving. Perhaps the young humped As- 

 planchna did not belong within the body of its seeming 

 parent. Perhaps it was some accidental inclusion forced 

 through some invisible aperture in the side of the larger 

 organism. In short, was it really in the uterus? Per- 

 haps it had been swallowed by the adult campanulate and 

 had managed afterward to tear its way through the 

 digestive tract, which latter organ had then healed and 

 allowed the prey to continue development in the body 

 cavity. 



While I was asking myself these questions and others, 

 I was also assiduously seeking for more examples, for if 

 the phenomena were regular more examples would cer- 

 tainly be found. 



A number were indeed discovered, and every possible 

 explanation was eliminated except that they were, as they 

 appeared to be, young humped rotifers which were pro- 

 duced by normal parthenogenetic development within the 

 giant campanulate type. I was able to discern, for some 

 of them, that they were within the uterus, and in every 

 way in normal position. The only slight sign of ab- 

 normality was that they usually seemed to be a little 

 small for the parental organism producing them; they 

 filled less of the body cavity than did corresponding 

 young that were developed true to type. But upon 

 second thought this was but one more sign of the com- 

 pleteness of the heterogenesis. These humped young 

 were developing of exactly the size that they would have 

 developed within the body of a humped parent; within 

 the body of a campanulate they naturally left room, so to 

 speak, to spare. The internal organs, too, of these 

 heterogenetic young bore out, in detail, the conclusion 

 suggested by the external appearance. The lighter 



