138 David Day Whitney 



ferent part of the ovary is not certain, but the evidence seems to 

 indicate that they are male eggs. 



In the two kinds of parthenogenetic eggs of some of the aphids 

 Stevens finds that there is no reduction in the number of the 

 chromosomes during the formation of the polar body. Lenssen, 

 in a study of the parthenogenetic eggs of the Rotifer, Hydatina 

 senta, finds that there is a reduction in the number of the chromo- 

 somes during the formation of the polar body in the male egg but 

 no reduction in the female egg. 



Weismann found that both kinds of parthenogenetic eggs of 

 Polyphemus (Daphnid), certain Ostracods and Rotifers produced 

 only one polar body while the fertilized eggs produced two polar 

 bodies. Blochmann and Stevens found the same relation to hold 

 for certain aphids. 



In Lisparis dispar, a parthenogenetic Lepidopteran, Platner 

 found that two polar nuclei were formed. In the bee apis, Bloch- 

 mann, Paulcke, Petrunckewitsch and others find that the partheno- 

 genetic eggs which develop into male animals give off two polar 

 bodies. In the Rotifer, Asplanchna, Mrazek, Erlanger and 

 Lauterborn found that the female parthenogenetic egg gave off 

 one polar body and that the male parthenogenetic as well as the 

 fertilized egg gave off^ two polar bodies. In the parthenogenetic 

 eggs of Hydatina senta Lenssen thought that the male egg gave 

 off one polar body and the female egg gave off none ! 



At the suggestion and under the supervision of Prof. T. H. 

 Morgan the following work upon the eggs of Hydatina senta was 

 done with the view of obtaining more light upon the maturation 

 stages and their relation to the determination of sex. 



I am also indebted to Prof. E. B. Wilson for many valuable 

 suggestions and criticisms. 



II MATERIAL AND METHODS 



The Rotifers were collected and reared in cultures as described 

 in a former paper. 



The first maturation spindle is formed before the egg is laid 

 and in order to study the early maturation stages animals con- 



