CHROMOSOMES OF HYDATINA SENTA. 6l 



I am not prepared to advocate any view as to the method by 

 which, in the absence of visible chromosome differences, a female- 

 producer is distinguished from a male-producer. It has been 

 suggested to me that there may be a difference in the chromatin, 

 perhaps a quantitative difference, which does not involve the 

 number of chromosomes. This possibility may be investigated 

 in other ways. If there is a single fundamental distinction 

 between the two kinds of females, any attempt to discover it 

 must take account of the fact that the distinguishing feature of 

 the female-producing parthenogenetic egg must also be an 

 attribute of the fertilized egg. 



LITERATURE CITED. 

 Lenssen, Dr. 



'98 Contribution a 1'etude du developpement et de la maturation des oeufs 



chez 1' Hydatina senta. La Cellule, T. 14, pp. 419-451. 2 pi. 

 '98 Contribution a 1'etude du developpement et de la maturation des oeufs 



chez 1' Hydatina senta. Zool. Anz., Bd. 21, pp. 617-622. 

 Morgan, T. H. 



'09 A Biological and Cytological Study of Sex Determination in Phylloxerans 



and Aphids. Jour. Exp. Zool., Vol. 7, pp. 239-353. i pi. 

 Shull, A. F. 



'12 Studies in the Life Cycle of Hydatina senta. III. Internal Factors In- 

 fluencing the Proportion of Male-producers. Jour. Exp. Zool., Vol. 12, 

 pp. 283-317. 

 Whitney, D. D. 



'OQ Observations on the Maturation Stages of the Parthenogenetic and Sexual 

 Eggs of Hydatina senta. Jour. Exp. Zool., Vol. 6, pp. 137-146. 



