' No. 548] A CASE OF POLYMORPHISM 451 



changed. This latter condition limits the range of pos- 

 sible experiment, but I could not once succeed in getting 

 Asplanchna to live and reproduce in any other than its 

 native fluid; 3 even dilution of one fourth with water from 

 some other source seemed in every case to preclude a suc- 

 cessful culture. In nature, too, every rain which diluted 

 to an appreciable extent the vile ponds in which this 

 Asplanchna flourishes results in the death of the entire 

 stock, which is only replaced by the hatching of new in- 

 dividuals from resting eggs. 



As to food, many organisms were tried, and a number 

 proved available. Best of all, for the smaller forms of 

 the Asplanchna, Paramecium proves an ideal food. 

 Other rotifers come next, of which I used especially Hy- 

 datina and Brachionus; while, surprising as it would 

 appear, the crustacean, Moina paradoxa, although a 

 large-sized member of its group, provides, under certain 

 circumstances, an available food supply for this over- 

 grown and voracious rotifer. The adult Moinas are not 

 eaten, but young and even half-grown individuals may 

 be regularly eaten by the mammoth campanulate form I 

 have described. The humped rotifers ingest the Crusta- 

 cea with difficulty, but succeed in doing so at times to a 

 considerable extent. 



Omitting further reference to methods, and refraining 

 from any attempt to describe the course of experiments, 

 I will briefly give their results, prefacing only that I make 

 no general statement which is not based on the outcome of 

 at least ten separate experiments or as ample observa- 

 tions in nature, or on both. 



The first of these results which I will state, although 

 nearly the last that I demonstrated, is the error of my 

 original conclusion in regard to the relationship betwen 

 the two types already described. The campanulate and 

 humped types do reproduce each other reciprocally, al- 

 though with very different frequency in the two direc- 



•This does not apply to cultures started from resting eggs. These may be 



