No. 549] 



A CASE OF POLYMORPHISM 



533 



quate. The individuals with smaller humps are always 

 transitional or degenerative in origin. 



But what could be the cause of the hypertrophy of 

 the humps to fully double their usual prominence, and 

 this in individuals that always gave evidence of starva- 

 tion? Such individuals occurred in certain cultures in 

 considerable numbers, and constituted a very extreme 

 type; the animals were always much more transparent 

 than any others, the body wall being thin and the internal 

 organs usually pale, shrunken, and undeveloped, the 

 stomach empty, and embryos lacking. The general body 

 form was extremely slender, with corona but two thirds 

 average width, while the ventral, or rather posterior, 

 hump was not only long, but developed a secondary pro- 

 longation, as it were, from the end of the original one. 

 Such animals swim, all but habitually, with the lateral 

 humps retracted, and in this condition are so slender as 

 hardly to suggest the genus Asphinchna, the form being 

 apparently more nearly that of Hydatina. But with the 

 thrusting out of the lateral humps a singular transforma- 

 tion occurs; these structures are so long that their ex- 

 panse equals or exceeds the animal's length, and so 

 slender that the animal's forward motion bends them 

 backward. In my notes I designated these extreme 

 animals as the " cross-bow type." 



As already mentioned, they occurred in considerable 

 numbers in several of my mass cultures. I also obtained 

 them several times under controlled conditions in isola- 

 tion experiments, but I found no clew to the cause of 

 their production until I discovered that they were fre- 

 quently produced by the gaint campanulates, and espe- 

 cially by the campanulates that were 3/otna-feeders. It 

 seemed Very striking that this variant, which carried the 

 development of the humped form to its utmost extreme, 

 should be thus produced by the robust companulates in 

 which there are no humps, and in which, indeed, all the 

 characteristics are at the farthest possible remove from 



