EFFECTS OF AMPHIMIXIS OS THE GERM-PLASM 



247 



correspondence with the absence of amphimixis. For the full 

 number of iclants only appears a second time in an ovum adapted 

 for fertilisation, by the union of the nucleus of the sperm-cell with 

 that of the ovum. 



RedU 



Fig. 20. — Diagram of the formation of spermatozoa in Ascnris megalocephala, var. 

 bivalens. (Modified from O. Hertwig.) — A, primitive sperm-cells; B, sperm- 

 raother-cells; C, first 'reducing division'; D, the two daughter-cells; E, second 

 ' reducing divisions'; F, the four granddaughter-cells (the sperm-cells). 



I consider this remarkable and apparently useless * process 

 of the doubling and two subsequent halvings of the idants as a 

 jftethod of still furtJier increasing the number of possible com- 

 binations of idants in the germ-cell of one and the same individ- 

 ual, and have given reasons for this opinion in the above-named 



* It might be supposed from the observations of Ruckert on the ovum of 

 the dog-fish, which were described in Chapters I. and II., that this doubling 

 is simply concerned with a doubling as regards mass, and consequently 

 with the activity of the idants : their activity must be very considerable in 

 this case, for the egg of the dog-fish is very large, and requires a consider- 

 able amount of multiplication of the ' oogenetic ' determinants. But a 

 doubling of the idants occurs also in all other animal eggs, even in the 



