TRANSMISSION THROUGH THE RESTING EGG OF 



EXPERIMENTALLY INDUCED CHARACTERS 



IN ASPLANCHNA AMPHORA^ 



CLAUDE W. MITCHELL AND J. H. POWERS 



The chief purpose of undertaking the experiments which form 

 the basis of this article was to ascertain whether or not the marked 

 modifications which may be experimentally induced in the above 

 rotifer are in any sense hereditary beyond the parthenogenetic 

 stages. As to what the modifications are in this remarkably 

 variable and tri-morphic species and as to the means by which they 

 are produced in nature as well as under experiment, we refer the 

 reader to the previous articles in the present series, as well as 

 to the publications of Lange, Powers, and Daday (see bibli- 

 ography) . We may state briefly that variation in this species is 

 shown to be, in last resort, entirely under the control of nutri- 

 tion; that in character it is deep-seated, pervasive, erratic, and 

 sudden — bearing all the ear-marks of mutation; and that it is 

 hereditary in a strong though variable degree throughout the 

 parthenogenetic series. 



In several respects variation in this rotifer appears like a 

 species-making process: The different types produced occur 

 erratically though sometimes abundantly in nature; their differ- 

 ences would be quite sufficient for specific distinction, and several 

 of the forms produced closely parallel types of the genus which 

 have been assumed to be definite species. N*evertheless it is 

 plain that we can not regard the variation of this Asplanchna as a 

 true species-forming process until it is proven that the variation 

 in question effects, in at least some degree, the sexual gametes. 

 However varied the parthenogenetic forms and however thor- 

 oughly it may be proven that this variation is a result of a modifi- 

 cation of the parthenogenetic ova, which transmits itself for 



' Studies from the Zoological Laboratory, The University of Nebraska, No. 110. 



347 



