SEX DETERMINATION — A SUGGESTION. 9 



Any egg then, which has completed its female phase, if 

 able to proceed with development without external inter- 

 ference such as fertilization, natural or artificial, should give 

 rise to a male. It is significant that wherever eggs undergo a 

 perfectly normal maturation and are then capable of develop- 

 ment with or without fertilization, as in Hymenoptera and 

 Kotifera, those eggs which develop without fertilization do 

 always give rise to males. The fact that these eggs have 

 matured normally is emphasised, because, in the light of recent 

 research, it seems possible that the readjustment between 

 nucleus and cytoplasm during the maturation of germ-cells 

 may not be necessarily a preparation for fertilization, but 

 may really mark the completion of successive phases of meta- 

 bolic activity. A foreshadowing of this process has been 

 demonstrated recently by Woodruff 21 and Erdmann in 

 Paramoecium, and has been shown to be a phenomenon which 

 occurs periodically quite apart from conjugation. A well- 

 marked rhythm occurs during the life history of Paramoecium, 

 a period of maximum activity in division alternating with a 

 period of minimum activity. When the minimum is reached 

 a readjustment takes place between cytoplasm and nucleus ; 

 division then proceeds with increasing rapidity to a maximum, 

 then gradually slows down to a minimum when readjustment 

 again takes place : and this without any conjugation whatever. 

 In Paramoecium we have no evidence that the phases differ 

 from each other in any way ; such evidence has never to my 

 knowledge been sought : but in Hymenoptera and Rotifera 

 it is an established fact that after the complete nuclear readjust- 

 ment which ends the female phase of the egg, the following 

 period of activity invariably gives a male. In most other 

 groups where parthenogenesis occurs, the eggs do not mature 

 normally, and they then give rise to females. The abnormal 

 maturation is usually looked upon as a device which, bv 

 causing the retention of the chromosome content usually 



