THEORY OF FERTILIZATION. i 49 



the union; others attack the deeper problem of the physiological 

 import of the process, — a problem the full solution of which is still 

 remote; while others have confined themselves rather to discussing the 

 uses of fertilization in relation to the species. Some representative 

 positions on each of these planes must be sketched; and, first of all, 

 the more morphological theories, and the very important question 

 whether the union of nuclei is everthing, or whether the union of cell- 

 substance has also its import. 



(a) Hertwig'' s View. — Professor O. Hertwig, who was one of the first 

 carefully to follow out the details of fertilization in animals, thus sums up his 

 " Theorie der Befruchtung" ': — " In fertilization, distinctly demonstrable 

 morphological processes occur. Of these the important and essential one is the 

 union of two sexually differentiated cell-nuclei, the female nucleus of the ovum 

 and the male nucleus of the sperm. These contain the fertilizing nuclear 

 substance, which is an organized substance, and acts as such in the process. 

 The female nuclear substance transmits the characters of the mother, the male 

 nucleus those of the father, to the offspring." The nucleus is thus the essential 

 element both in fertilization and in inheritance. 



(b) Strasburger' s View. — What Hertwig maintains for animals, Strasburger 

 does for plants. "The process of fertilization depends upon the union of the 

 sperm nucleus with the nucleus of the egg-cell ; the cell-substance (cytoplasm) 

 does not share in the process." "The cell-substance of the pollen-grain is only 

 the vehicle to conduct the generative-nucleus to its destination." It may 

 become nutritive, he allows however, to the germ-rudiment. "Generally the 

 uniting nuclei are almost perfectly alike," though there may be slight differences 

 in the size of the nucleoli. "The two cell-nuclei do not differ in their nature, 

 they are not sexually differentiated in the ways that the individuals are from 

 which they originate. All sex-differentiations only serve to bring together the 

 two nuclei essential to the sexual process." 



The opinions of these two authorities are certainly representative, and they 

 both agree in emphasizing that the nuclei are all-important, and that it does not 

 matter much about the union of cell-substance. Some objections to this view 

 must be noticed, {a) It is permissible to doubt whether the recent concentration 

 of attention upon the nucleus has not led to some under-appreciation of the 

 general protoplasm. In the permanent conjugation of two cells, the entire 

 contents of the two cells are obviously fused ; and even when the union is 

 temporary, Joseph has observed what looks like an interchange of protoplasmic 

 as well as of nuclear substance, {b) There are a few observers still, such as 

 Nussbaum, who maintain that in fertilization in animals the substance of the 

 sperm is important as well as its nucleus, (r) Strasburger notes the minimal 

 quantity of cell-substance so often present round the male nucleus, and urges 

 that if it were important there would surely be more of it. But it is quite 

 conceivable that a minimal quantity of highly active protoplasm might have, like 

 a ferment, a momentous influence on a large quantity of a different character. 

 (c() The researches of Boveri show that though the union of nuclei is so essential, 

 the protoplasmic activity and share in the process are also considerable. It 

 appears to us a fact well worthy of consideration, that according to this 

 authority the sperm brings with it into the ovum a protoplasmic center — a 

 "centrosoma" — which appears to be of much importance in the preparation 



