IV.] FOUNDATION OF A THEORY OF HER EDI TV. 245 



these very aquaria an undisturbed growth of different algae 

 was flourishing, so that there could have been no deficiency, 

 but, on the contrary, a great abundance of nutritive material. 

 I may add that since that time I have conducted some experi- 

 ments directly bearing upon this question, by bringing virgin 

 females as near to the verge of starvation as possible, but in no 

 case did they enter upon sexual reproduction \ 



An author must have been to some extent misled by pre- 

 conceived ideas when he is unable to see that the manner in 

 which the two kinds of eggs are respectively formed, directly 

 excludes the possibility of the origin of sexual eggs from the 

 effects of deficient or poor nutrition. The resting eggs, which 

 require fertilization, are always larger, and require for their 

 formation far more nutritive material, than the parthenogenetic 

 summer-eggs. In Moiiia, for instance, forty large food-cells are 

 necessary for the formation of a resting ^gg^ while a summer- 

 egg only requires three. And Dusing is aware of these facts, 

 and quotes them. How can the formation of resting eggs 

 depend upon the effects of poor nutrition when food is most 

 abundant at the very time of their formation? In all those 

 species which inhabit lakes, sexual reproduction occurs to- 

 wards the autumn, and in such cases the resting eggs are true 

 winter-eggs, destined to preserve the species during the winter. 

 But at no time of the year is the food of the Daphnidae so 

 abundant as in September and October, and frequently even 

 until late in November (in South Germany). At this period of 

 the year, the water is filled with flakes of animal and vegetable 

 matter in a state of partial decomposition, thus affording 

 abundant food for many species. It also swarms with a large 

 number of species of Crustacea, Radiolaria, and Infusoria; and 

 thus such Daphnids as the Polyp/wiuichie are also well provided 

 for. Hence there is no deficiency in the supply of food. Any 

 one who has used a fine net in our fresh waters at this time of 

 the year must have been at first astonished at the enormous 

 abundance of the lower forms of animal life ; and he must have 

 been much more astonished if he has been able to compare 

 such results with the scanty population of the same localities 

 in spring. But it is during the spring and summer that tiicse 



1 I intend to publish these experiments elsewhere in connexion with 

 other observations. 



