Varietäten, Descendenz, Hybriden. 255 



tound to be shorter and narrower, and less variable in both length 

 and breadth. They were also relatively more slender, more variable 

 in shape of bod3% and have the length and breadth less highly cor- 

 related than the non-conjugants. 



The correlation between the two members of a pair of conju- 

 gants was very considerable , being on the average about 0.6. The 

 author believes that this homogamic correlation arises as the result 

 of the necessity for the mouths of the two individuals to come toge- 

 ther (or "fit") when the extreme anterior ends are united. And he 

 points out the possible importance of such homogamy as a means of 

 leading tot divergent evolution. He finds further that there is a diffe- 

 rentiated "Conjugant tj'pe" wich is relatively fixed and constant 

 under varying conditions of environment, as compared with the 

 general type of the population in fission generations. R. H. Lock. 



Punnett, R. C, Sex Determination in Hydatina, with some 

 remarks on parthenogenesis. (Proc. Roy. Soc. London. B. 

 LXXVIII. 524. p. 223— 23L 1906.) 



The author has applied Mendel's principle of breeding from 

 individuals to the parthenogenetically reproducing animal Hydatina 

 se)ita. Three kinds of ova are produced by this rotifer viz: (1) parthe- 

 nogenetic ova which develop into females, (2) parthenogenetic ova of 

 smaller size which develop into males, and (3) fertilized eggs which 

 develop into females. 



It appears that impregnation of females producing the first kind 

 of eggs (thelytokous females) leads to no result, but if females which 

 would otherwise produce (2) (arrenotokous females) are impregnated 

 at an earl}^ age they give rise to 3 instead of to 2. 



Authors have supposed that change of conditions such as tempe- 

 rature and nutrition may affect the relative numbers of thelytokous 

 and arrenotokous individuals among the offspring of thetytokous 

 females. The present author's experiments on the other hand lead 

 him to conclude that among the rotifers used three different types 

 of thelytokous females occured viz: 



A. Females producing a high percentage of arrenotokous females. 



B. Females producing a low percentage of arrenotokous females. 



C. Purely thelytokous females producing no arrenotokous females. 

 And no evidence could be found to show that either temperature or 

 nutrition had any effect in determining the production of arrenoto- 

 kous females. 



The author concludes that the facts can only be explained on 

 the supposition that there are inherent differences in the zygotic 

 Constitution of individual females: more than one kind of egg must 

 in fact be produced by the same individual in certain cases. For 

 this reason, and also in consideration of the enormous mass of orga- 

 nised substance theoretically producible by such a parthenogenetically 

 reproducing organism without any external process of fertilisation , 

 the Suggestion is made that in a parthenogenetic animal a process 

 of gametogenesis takes place followed by an internal fusion of pairs 

 of gametes: that such an organism is in fact really hermaphrodite 

 and seif impregnated. And the höpe is expressed that the matter 

 may be taken up by the histologists. R. H. Lock. 



