244 THE CONTINUITY OF THE GERM-PLASM AS THE 



possess an ovogenetic nucleoplasm of a somewhat different mole- 

 cular structure from those germ-cells which have only to form 

 a few large blue fat-globules, as in the summer-eggs of the same 

 species. It is further probable that different proportions obtain be- 

 tween germ-plasm and ovogenetic nucleoplasm, in these two kinds 

 of germ-cells ; and it would be a very simple explanation of the 

 otherwise obscure part played by the food-cells, if we were to 

 suppose that they do not contain any germ-plasm at all, and on 

 this account do not enter upon embryonic development, but are 

 arrested after growing to a certain size. Such an explanation, 

 however, would not by itself show why they subsequently undergo 

 gradual solution in the surrounding fluids. But since we know 

 that egg-cells also begin to undergo solution as soon as the parent 

 Daphnid is poorly nourished, we can hardly help also referring the 

 solution of the food-cells to insufficient nourishment, occurring as 

 soon as the egg-cell, after the attainment of a certain size, exercises 

 a superior power of assimilation. But hitherto we could not in any 

 way understand why the third out of a group of germ-cells should 

 always gain this superior power and become an egg-cell. If it 

 could be shown that its position is more highly favoured in respect 

 of nutrition, we could understand why it outstrips the other three 

 in development, and thus prevents them from further growth. 

 But nothing of the kind can be shown to occur with any degree of 

 probability, as I have previously mentioned in my works on the 

 subject. At that time, having no better explanation, I adopted 

 the view in question, although only as a provisional interpreta- 

 tion. It was not possible for me to seek in the substance of 

 those four apparently identical cells for the cause of their different 

 development ; but now I am justified in offering the supposition 

 that during the division of a primitive germ-cell into two, and after- 

 wards into four germ-cells, an unequal division of the nucleoplasm s 

 takes place, in that one of the four cells receives germ-plasm as 

 well as ovogenetic nucleoplasm, while the other three receive the 

 latter alone. Similarly, the fact that the second cell of the group 

 may occasionally become an egg is also intelligible, although this 

 fact remained quite inexplicable by my former interpretation. The 

 fact that true egg-cells, or even the whole ovary with all its germ- 

 cells, may break up and become absorbed when the animal has been 

 starved for a certain period of time, seems to me to be no objection 



