246 THE CONTINUITY OF THE GERM-PLASM AS THE 



The only objection which can be raised against this conclusion 

 depends upon the supposition that the nucleoplasm of the sperm- 

 cell is qualitatively different from that of the egg-cell. I have 

 already dealt with this view, but I should wish to refer to it again 

 rather more in detail. Some years ago I expressed the opinion l 

 that the physiological values of the sperm-cell and of the egg-cell 

 must be identical ; that they stand in the ratio of I : I. But 

 Valaoritis 2 has brought forward the objection that if we consider 

 the function of a cell as the measure of its physiological value, it is 

 only necessary to point to the respective functions of ovum and 

 spermatozoon in order to show that their physiological values must 

 be different. ' The egg-cell alone, by passing more or less com- 

 pletely through the phyletic stages of the female parent, developes 

 into a similar organism ; and although the presence of the sperma- 

 tozoon is in most cases required in order to render possible such a 

 result, the cases of parthenogenesis prove nevertheless that the 

 egg can do without this stimulus.' This objection appeared to be 

 fully justified as long as fertilization was looked upon as the ' vital- 

 ization of the germ,' and so long as the sperm-cell was considered 

 as merely 'the spark that kindles the gunpowder,' and further 

 so long as the germ-substance was believed to be contained in the 

 cell-body. But now we can hardly give to the body of the egg- 

 cell a higher significance than that of the common nutritive 

 soil of the two nuclei which conjugate in fertilization. But 

 these two nuclei ' are not different in nature,' as Strasburger says, 

 and as I fully believe. They cannot differ in kind, for they both 

 consist of germ-plasm belonging to the same species of animal or 

 plant ; and there cannot be any deeper contrast between them such 

 as would correspond to the differences between mature individuals. 

 They cannot, from their essential nature, exercise any special at- 

 traction upon each other, and when we see that sperm-cell and egg- 

 cell do nevertheless attract each other, as has been shown in both 

 plants and animals, such a property must have been secondarily 

 acquired, and has no other significance than to favour the union of 

 sexual cells an arrangement which may be compared to the vi- 

 brating flagellum of the spermatozoon or the micropyle of the egg, 

 but which is not fundamental, and is not based upon the molecular 



1 ' Zeitschrift fur wissenachaftliche Zoologie,' Bd. XXXIII. p. 107. 1873. 

 3 Valaoritis, 1. c., p. 6. 



