250 CONTTXUITY OF THE GERM- PLASM AS THE [IV. 



apparently identical cells for the cause of their different de- 

 velopment ; but now I am justified in offering the supposition 

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

 afterwards into four germ-cells, an unequal division of the 

 nucleoplasms 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 ^^'g 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 to our present 

 view, any more than the fact that an Infusorian may die from 

 star\'ation would be an objection to the supposition of the im- 

 mortality of unicellular organisms. The growth of an organism 

 is not only arrested by its constitution, but also by absolute 

 want of food ; but it would be very foolish to explain the dif- 

 ferences in size of the various species of animals as results of 

 the different conditions of nutrition to which they were subject. 

 Just as a sparrow, however highly nourished, could never attain 

 the size or form of an eagle, so a germ-cell destined to become 

 a summer-egg could never attain the size, form, or colour of 

 a winter-egg. It is by internal constitutional causes that the 

 course of development is determined in both these cases ; and 

 in the latter, the cause can hardly be anything more than the 

 different constitution of the nucleoplasms. 



All these considerations depend upon the supposition that 

 the egg-nucleus contains two kinds of idioplasm, viz. germ- 

 plasm and ovogenetic nucleoplasm. I have not hitherto brought 

 forward any direct evidence in favour of this assumption, but I 

 believe that such proofs can be obtained. 



It is well known that there are certain eggs in which the polar 

 bodies are not expelled until after the entrance of spermatozoa. 

 Brooks ^ has already made use of this fact as evidence against 

 Minot's and Balfour's theory; for he quite rightly concludes 

 that if the polar bodies really possess the significance of male 

 cells, we cannot understand why such eggs are unable to 

 develope without fertilization, when they still possess the male 



' Brooks, ' The Law of Heredity.' Baltimore, 1883, p. 73. 



