224 



Mr. R, C. Punnett. 



[May 15, 



In a r series of brief papers communicated to the French Institut, Maupas* 

 held that temperature was the factor which determined the result, but 

 that it produced an effect only in newly -hatched $ 's before the eggs had 

 commenced to develop in the ovary. To quote his words : " Au debut de 

 l'ovogenese, au contraire, l'oeuf est encore neutre et, en agissant convenable- 

 ment, on peut a ce moment lui faire prendre a volonte" l'un ou l'autre 

 caractere sexuel. L'agent modificateur est la temperature. L'abaisse-t-on 

 les jeunes ceufs qui vont se former revetent l'etat de pondeuse d'oeufs 

 femelles ; l'eleve-t-on, au contraire, c'est l'etat de pondeuse d'oeufs males qui 

 se developpe." 



More recently Nussbaumf has criticised Maupas' results. He has pointed 

 out that under adverse nutritive conditions the eggs laid by a thelytokous 

 ? are often no larger than those laid by an arrenotokous ? under normal 

 conditions. Such adverse conditions Maupas must have brought about by raising 

 the temperature, and Nussbaum suggests that Maupas mistook the small ? eggs 

 then produced for $ eggs. Had he waited for them to hatch he would have 

 realised their true nature. From my own experience, in so far as it goes, 

 I am inclined to attribute some weight to this criticism of Nussbaum, and 

 to agree with him in considering that an element of uncertainty is in this 

 way introduced into Maupas' results. 



Nussbaum supported his criticism by experiments and showed that a ? 

 subjected to a high temperature before hatching or during the earlier period 

 of its life may give rise to thelytokous $ 's only (Experiments 21, 23, and 

 24, pp. 265 to 267). 



Having rejected temperature as a factor in the determination of sex in 

 Hydatina, Nussbaum turned his attention to other possible influences, and 

 believed that he had found such a one in nutrition. 



" Bei Hydatina senta bestimmt wahrend einer gewissen Entwicklungsphase 

 die Ernahrung das Geschlecht des ganzen Geleges eines jeden jungfraulichen 

 Weibchen. Wird das auskriechende Weibchen bis zur Eeifung seines 

 ersten Eies gut ernahrt, so legt es nur weibliche Eier ; wird es bis zur 

 Geschlechtsreife mangelhaft ernahrt, so legt es nur mannliche Eier. Vor 

 und nach dieser Periode hat die Ernahrung keinen Einfluss " (p. 306). 



In such a conclusion I cannot agree with Nussbaum, for reasons which 

 will appear below. It is sufficient to note here that his own experiments do 

 not always bear him out. Thus in Experiment 50, p. 283, he had a 

 " Hungercolonie " on October 4, in which were many $ eggs. From the 

 account it is evident that many of these must have hatched and have been 



* ' Comptes Rendus,' 1890-91. 

 t ' Archiv f. mik. Anat.,' 1897. 



