THE BEARERS OF THE HERITAGE 



2QS 



in which a single large, primordial germ-cell (p. g. c.} has already been 

 set apart at one end of the developing embryo. The nuclei of the rest 

 of the embryo still lie in a continuous protoplasmic mass which has 

 not yet divided up into separate cells. The densely stained nuclei at 

 the opposite end of the section are the remnants of nurse-cells which 

 originally nourished the egg. Fig. 45, B, is a longitudinal section 



oeJg 



FIG. 45. A, germ-cell (p.g.c.) set apart in the eight-celled stage of cleavage 

 in Miastor americana. (After Hegncr.) The walls of the remaining seven somatic 

 cells have not yet formed, though the resting or the dividing (M p) nuclei may be 

 seen; c R, chromatin fragments cast off from the somatic cells; B, section length- 

 wise of a later embryo of Miastor; the primordial egg-cells (oog 3 ) are conspicuous. 

 (From Guyer, after Hegner.) 



through a later stage in the development of Miastor; the primitive 

 germ-cells (oog) are plainly visible. Still other striking examples 

 might be cited. Even in vertebrates the germ-cells may often be 

 detected at a very early period. 



Significance of the early setting apart of the germ-cells. It is of 

 great importance for the reader to grasp the significance of this early 

 setting apart of the germ-cells because so much in our future discussion 

 hinges on this fact. The truth of the statement made in a previous 

 chapter that the body of an individual and the reproductive substance 



