Evidence from Metazoan Germ-Cells 19 



tending about half way around the egg just below the 

 equator (figure 43c. yji.) This position it retains through- 

 out the whole development, giving rise to the muscle and 

 mesenchyme cells (figure 43 d. cr.) 



"20. . . . At the close of the first cleavage (figure 43d) 

 the nuclei and clear protoplasm move (c.p.) into the upper 

 hemisphere and thereafter, throughout development, this 

 hemisphere contains most of the clear protoplasm and gives 

 rise to the ectoderm. 



"21. . . . When the clear protoplasm moves into the 

 upper hemisphere the yolk is largely collected in the lower 

 hemisphere. This yolk-rich area gives rise to the endoderm. 



"24. The chief factor of localization is protoplasmic 

 flowing ; cell division is a factor of subordinate value." 7 



From the numbers given in this quotation it will be recog- 

 nized that only a portion of the summing up of results is 

 here presented; and it will be understood that each item in 

 the summary represents a lengthy, detailed description in 

 the body of the memoir. This summary we may again sum- 

 marize as follows : By the time the first division of the egg- 

 cell is completed the portions of the egg which are to give 

 rise to three great groups of tissues of the future animal 

 are distinguishable from one another by definitely visible 

 attributes. The clear protoplasm situated at the upper 

 pole of the cell will give rise to the external epithelium or 

 skin; the yolk-laden protoplasm in the lower hemisphere will 

 produce the epithelial lining of the digestive tract ; and 

 from the yellow protoplasm gathered on the surface at the 

 lower pole will come most of the muscle and connective tis- 

 sue of the animal. 



(b) Conklin's Interpretation 



Passing now to a consideration of these facts in relation 

 to heredity we must not neglect to notice the two-fold aspect 



