SEX-DETERMINATION IN ASPLANCHNA AMPHORA^ 



CLAUDE W. MITCHELL 



University of Nebraska 



INTRODUCTION 



While studying the polymorphic rotifer, Asplanchna amphora, 

 and while seeking to ascertain the factors which determine its re- 

 markable transitions of form, attention was directed again and 

 again to the value of this species as material for the study of 

 sex-determination in rotifers. It was in the genus Asplanchna 

 that male rotifers were first discovered and few other genera pro- 

 duce them in so great numbers. The species in question is 

 hardy, easily reared, and capable of being subjected to a great 

 variety of conditions. Especially in the matter of feeding, its 

 polyphagous habits are well known, and are productive of marked 

 physiological and morphological results. Of special significance 

 is the fact that the polymorphic character of the species itself, 

 mirroring as it does marked underlying differences, it is of ut- 

 most use in following any and all effects of controlled conditions. 

 Thus the production or non-production of males does not occur 

 as a fact which stands alone but as the concomitant of morpho- 

 logical changes which may be of much value in determining its 

 cause. 



Finding the material thus favorable it was suggested by Dr. 

 J. H. Powers that experiment be undertaken along this line, in the 

 hope that work upon this unstudied species might aid materially 

 the solution of the problem which has hitherto been attempted 

 solely upon a single rotifer, namely, Hydatina senta. I wish 

 again to thank Dr. Powers for his valuable suggestions and aid, 

 but above all for the interest shown in each experiment and in 

 the results of the entire work. 



1 Studies from the Zoological Laboratory, University of Nebraska, No. 109. 



225 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 15, NO. 2 



