446 THE AMEBIC AN NATURALIST [Vol. XL VI 



musculature, the narrower ovary- or shell-gland, were 

 obviously characteristic of the smaller humped type. 

 Most definite of all, however, was the evidence of the 

 trophi. These are universally recognized as yielding 

 characters of specific rank. They are wholly developed 

 before birth, and they were very different in the two 

 types in question. I used, therefore, the utmost pains to 

 ascertain the nature of the trophi in these heterotypic 

 young. The result was without question; the trophi in 

 every case indicated a complete and sudden transition 

 from the campanulate to the smaller humped type. This 

 was true both in regard to size and in details of structure. 



I concluded, then, after the study of every organ which 

 I could make out with clearness in the material at my 

 disposal, that these atypic young in the large campanu- 

 late Asplanchna represented, not an ordinary variation, 

 but the sudden production of one type by another and 

 quite distinct one. 



But a number of questions suggested themselves at 

 this point. In what number were these mutants, if such 

 they really were, being produced? Was the production 

 of one type by the other occurring in both directions, or 

 only in the one in which I had chanced to find it? And, 

 again, could transition specimens or any signs of grada- 

 tion between the two types be found among the adults, 

 or individuals of any age, in the material at hand? 



As to the first question, I examined carefully 270 

 mounted adults of the giant campanulate type. Nearly 

 all were in reproduction, but only 90 of them contained 

 young sufficiently advanced in development and suffi- 

 ciently well placed to allow a certain judgment as to their 

 type. Of the 90 unborn young nearly one fourth (22) 

 were indisputably of the humped type, while 68 were just 

 as certainly of the parental or campanulate type. Noth- 

 ing should be made here of the ratio of one fourth and 

 three fourths. The phenomena in question are not the 

 result of a cross, and, moreover, the determination hinges 

 upon several factors; for one thing, upon my caution, 



