IIOLOBLASTIC AND MEEOBLASTIC SEGMENTATION. 



Ill 



the upper pole than the lower, and marks the line of division 

 between the upper and smaller portion of the egg from the lower 



FIG. 104. Unequal segmentation of the Frog's egg (after Ecker) in ten successive stages. 



and larger portion, in which the segmentation proceeds much more 

 slowly than in the former. 



In partial segmentation we find a sharply marked contrast between 

 the formative and 

 nutritive parts of the -" 



egg, inasmuch as the 

 latter does not seg- 

 ment. The terms 

 holoblastic and me- 

 roblastic therefore 

 have been applied to 

 total and partial seg- 

 mentation respec- 

 tively. 



Nevertheless, in 

 total segmentation 

 also, either groups of 

 segments of a definite 

 quality, or, at any 

 rate, a fluid yolk 

 material may be used 

 for the nourishment 

 of the developing 

 embryo. In fact, the 

 contents of every egg consists of two parts (1) of a viscous albu- 

 minous protoplasm; and (2) of a fatty granular matter, the 

 deutoplasm, or food yolk. The first is derived from the protoplasm 



FIG. 105. Segmentation of the germinal disc of a Fowl's egg, 

 surface view (after Kolliker). A, germinal disc with the 

 first vertical furrow ; B, the same with two vertical furrows 

 crossing one another at right angles ; C and I), more ad- 

 vanced stages with small central segments. 



