248 



THE GERM-PLASM 



essay. As already stated, a single halving of four idants can 

 only result in six combinations. But if, as actually occurs, each 



Red.][ 



Fig. 21. — Formation of ova in Ascnris vtegalocephala, var. bi7'alens. — A, primi- 

 tive germ-cell ; B, fully-developed egg-cell, the number of the idants in which have 

 increased from four to eight ; C, first ' reducing division ' ; D, the egg with the first 

 polar-body, immediately succeeding the stage represented in C; E, the first polar- 

 body has divided into two daughter-cells (2 and 3), the four idants which remain 

 in the egg giving rise to the second ' reducing spindle '; F, stage immediately suc- 

 ceeding the second 'reducing division' — i, the ripe egg-cell; 2, 3, and 4, the 

 three polar-cells; each of the four cells only containing two idants. 



smallest — in which a very small amount of yolk is contained — as well as in 

 the sperm-mother-cells, which never attain to such a size or structural dif- 

 ferentiation as do the ova. The process cannot be concerned with an in- 

 crease of the germ-plasm contained in the idants, for in the formation of the 

 ova three-quarters of the mass of germ-plasm passes into the polar bodies 

 and is again lost. The explanation of the process here given seems there- 

 fore to be the only possible one. 



