240 THE CONTINUITY OF THE GERM-PLASM AS THE 



starvation as possible, but in no case did they enter upon sexual 

 reproduction l . 



An author must have been to some extent misled by preconceived 

 ideas when he is unable to see that the manner in which the two 

 kinds of eggs are respectively formed, directly excludes the possi- 

 bility 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 Moina, for 

 instance, forty large food-cells are necessary for the formation of 

 a resting egg, while a summer-egg only requires three. And 

 Diising 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 

 towards 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 Dapknidae 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, 

 Eadiolaria, and Infusoria ; and thus such Daphnids as the Poly- 

 phemidae 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 

 these very Dapknidae reproduce themselves parthenogenetically. 

 I am far from believing that my experiments on Daphnidae are 

 exhaustive and final, and I have stated this in my published 

 writings on the subject ; but it seems to me that I have established 

 the fact that direct influences, whether of food or of temperature, 

 acting upon single individuals, do not determine the kind of eggs 



1 I intend to publish these experiments elsewhere in connexion with other 

 observations. 



