43 



opposite to that which happt'iunl in the worm Dinophilus. Issaliowitsch 

 sliows that teiuijeratur(s acted merely as iutlueiicing uutritiou, for wlieu tlie 

 animals were starved by being reared in distilleil water, males and resting 

 eggs were developed It'roni liis experiments it would seem that, so far as 

 parthenogenetic eggs were concerned, nutrition may act as a sex-determin- 

 ing factor. Both von Malseu and Issalvowitsch looli upon nutrition as a 

 sex-determining factor from the influence it is supposed to produce upon the 

 plasmic relation in the nucleus, as set fortli by Richard Hertwig. 



The more recent researches of Punnett upon Hydatena seem to throw 

 new light upon the subject in that they point out probable errors in the 

 studies of Maupas and Nussbaum {R. C. Punnett: Sex-determination in 

 Hydatena, with some remarks on parthenogenesis. Proc. Royal Soc, Series 

 B., 78: 223, 19(>6). In Hydatena three kinds of females may be recognized 

 by the kinds of eggs tliey lay: (a) females which produce females par- 

 thenogeneticalJy (thelytokous females) ; (b) females which produce males 

 parthenogeneticalJj' (arrenotokous females) ; and (c) the layers of fertil- 

 ized eggs. Of the first class of females, Punnett recognized from pedigree 

 cultures three different types. A. Females giving rise to a high percentage 

 of male producing individuals (arrenotokous females). B. Females giving 

 rise to a low percentage of male producing individuals. C. Purely female 

 producing individuals (pure thelytokous females). 



In experiments designed to test the effect of temperature and nutrition, 

 it was found that in the purely female producing individuals (class C), 

 no male producing forms appeared, the strain remaining pure, and that in 

 the class B, the ratio of males was not raised as a result of starving. Con- 

 sequently it is difficult to see tliat either temperature or nutrition has any 

 influence in determining male producing forms. Punnett suggests "that 

 the females, producing females parthenogeneticaliy (thelytokous), are 

 really hermaphrodite, though the male gametes may not exhibit the 

 orthodox form of spermatozoa. Such a view would account for the ob- 

 served absence of polar bodies in the female eggs, for it must be supposed 

 that the process of reduction and fertilization takes place before the 

 accumulation of yolky material." It may be added also that if no polar 

 bodies are formed, there is no reduction in the number of chromosomes, and 

 we may have, as has been clearly shown in certain plants, not a case of 

 parthenogenesis but one of apogamy. Whitney (Whitney, David Day. 

 Determination of sex in Hydatena senta. Jrnl. Exp. Zool., 5: 1-26, 1907). 

 in a still more recent study of Hydatena senta, finds that neither tempera- 



