PARENT-CELL AND PARENT-KEENEL. 1 7/ 



summed up in the word "life," is naturally entirely dif- 

 ferent from that of the two distinct ancestral cells, the 

 amalgamation of which gave rise to the parent-cell. The 

 life of the parent-cell (Cytula) is the jproduct or resultant 

 of the paternal activities, transmitted through the sperni- 

 oell, together ^uith the maternal activities, transmiitted 

 through the egg -cell. 



All good recent observations agree in showing tha.t 

 the individual evolution of man and of other animals 

 begins with the formation of such a parent-cell, and that 

 in the course of further evolution this then separates 

 by self-division, or cleavage, into a number of cells, the 

 so-called cleavage-globules or cleavage- cells (segmentella). 

 But the most active strife is still waged over the question 

 of the mode in which the parent-cell (cytula) originates, 

 and of the relative parts played by the sperm-cell and the 

 egg-cell in the formation of the parent-cell and in the act 

 of fertilization. Formerly it was usually assumed — and 

 many well-known naturalists still adhere to this — that the 

 original kernel (nucleus) of the egg-cell (p. 136, Fig. 11), 

 the so-called germ-vesicle, is retained unaltered during 

 fertilization, and that it directly transforms itself into the 

 parent-kernel, "the kernel of the first cleavage-globule." 

 But most more recent observers (with whom I agree) have 

 become convinced that the germ-vesicle, the original egg- 

 kernel, sooner or later disappears, and that the parent- 

 kernel (cytococcus) forms itself" anew. Here again, even 

 the question as to the time and mode in which the ne\^' 

 kernel of the parent-cell forms is at present still much 

 debated. Some assume that the germ- vesicle disappears 

 before fertilization, others say that this happens after ferti- 



