THE FERTILIZATION OF THE OVUM. 



31 



is carried into the eg-g, and is there absorbed, used as food, by 

 the cytoplasm of the ovum. On the ground of direct observa- 

 tion, the fusion of the general cytoplasm of the sperm with 

 that of the ovum can neither be affirmed nor denied in most 

 cases ; but it is a matter of observation that there is a union 

 of those portions of the cytoplasm which can be followed, viz., 

 the asters, and in view of what we know of conjugation among 

 the simplest animals and plants, where there is a fusion of 

 the cell-bodies as well as of the nuclei, I question whether 

 the cytoplasm which the sperm carries into the ovum, in the 

 case of Ascaris, merely degenerates and serves as food for the 

 egg cytoplasm. It seems to me more probable that this sperm 

 cytoplasm does not act as so much dead matter, but that it also 

 takes part in this union of the essential constituents of the two 

 cells. 



On a priori ground, I think we ought to expect that in fer- 

 tilization all the essential parts of one cell would unite with 

 corresponding parts of another cell. In fact, the form of 

 fertilization characteristic of the higher animals and plants 

 is generally supposed to have been derived from a condition 

 similar to that which at present obtains among the lower 

 animals and plants in which there is a fusion of two entire 

 cells. Most persons would probably agree that fertilization 

 consists in the union of the essential parts of two cells ; the 

 question is, "What are essential parts.'" It is known that if 

 some of the Infusoria are cut to pieces so that some of the 

 pieces contain portions of the nucleus, while others do not, the 

 nucleated portions will regenerate all the lost parts, while those 

 pieces which contain no part of the nucleus do not regenerate 

 but sooner or later perish. It is, therefore, certain that the 

 cytoplasm cannot perform the normal funtions of growth and 

 regeneration apart from the nucleus. It seems equally certain, 

 although much more difficult of demonstration, that the nucleus 

 cannot perform all its normal functions apart from the cyto- 

 plasm. Both nucleus and cytoplasm are essential constituents 

 of the cell, and one cannot be said to be more important than 

 the other. In spite of the assumption of smaller structural 

 units within the cell (such as the biopJiors of Weismann, the 



