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THE AMERICAN NATURALIST [Vol. XLVI 



physiologically or morphologically. Some stocks seem 

 larger than others from the start, and apparently gave 

 rise more readily to the second and third types. It will 

 require much careful experiment to ascertain the cause of 

 these diversities, and whether a tendency toward the 

 transmission of variations actually lies in the resting egg. 



If such proves to be the case, light will be immediately 

 thrown upon the farther problem, namely, whether the 

 saltations here described are intimately related to a true 

 species-making process. All in all, it seems that they 

 probably are thus related, especially as the forms pro- 

 duced parallel so closely other types of the genus which 

 are now universally regarded as definite and circum- 

 scribed species. 



But are these other types of the genus definite and cir- 

 cumscribed species, or are they (some of them at least) 

 but semi-independent types, occasionally brought into 

 existence by unusual nutritive conditions and then main- 

 taining for a time only their partial or complete auton- 

 omy? Unfortunately these remaining forms of the 

 genus are not accessible in the writer's vicinity. But 

 they would seem well worthy of careful study, both ob- 

 servational and experimental, where they may be found, 

 and it seems to the writer that such study, sufficiently 

 prolonged, will bring to light a species-making process 

 in rotifers which is somewhat different from any as yet 

 demonstrated in the animal kingdom. 



It is just possible that these saltational phenomena may 

 be purely local, or at least greatly exaggerated in the 

 genus Asplanchna. The food reactions of this genus are 

 undoubtedly extreme, and the development of their par- 

 thenogenetic ova in close proximity to this spasmodic 

 and very variable nutritive supply may possibly make 

 this genus exceptional. But no fundamental organic phe- 

 nomenon is wholly isolated and unlike the phenomena of 

 other species. If nutrition can modify the germ cells in 

 the genus Asplanchna and thus bring into existence new 

 types, nutrition surely must be a factor on a wider scale. 



