THE EGG- CELL OR OVUM. 101 



in the second polar globule is supplied by the fertilizing sperm. The beginning 

 of development depends upon the presence of a definite quantity of germ- 

 plasma. This the normal egg attains by first losing half and then regaining it, 

 while the parthenogenetic egg attains the same result by never losing any at all. 



In this, too, there is much hypothesis. The two kinds of nuclear plasma, the 

 difference between the two polar globules, the necessity for a definite quantity 

 before development begins, are all assumptions. Nor is it at all evident how the 

 advantage of fertilization (as a source of progressive change and so on) could 

 operate so as to induce the ovum to go through the circuitous process of losing 

 half its "germ-plasma," and then gaining it again. 



(d) It appears simpler to us to suppose that the ovum, like any other cell, 

 tends to divide or bud at the limit of growth, — a view in no way inconsistent 

 with regarding the process as an extrusion of male elements. The precise 

 homologies of the process will be clearer on reference to the diagram at 

 page 1 08. 



