86 REMARKS ON CERTAIN [XI. 



f::^g of A scan's megalocephala^ the observations of Strasburger 

 on the fertilization of the egg-cell in phanerogams by means of 

 the nucleus alone, and the experiments of Nussbaum and 

 Gruber on the artificial division of Infusoria. To these may be 

 added certain other considerations of essential importance, viz. 

 the occurrence of karyokinesis, and the fact that the formation 

 of polar bodies by the ova of animals can be rendered intel- 

 ligible only on the assumption that the idioplasm resides in the 

 nucleus. The formation of polar bodies involves the division 

 of the nuclear substance of the egg into two halves similar in 

 quantity, but the cell-body itself is divided into two entirely 

 dissimilar portions, the relative sizes of which differ in different 

 species. The essential part of this expulsion of polar bodies 

 from the ovum, must lie in the division of the nuclear substance, 

 and not in the division of the cell. These facts and considera- 

 tions, in conjunction with others, completely convinced me that 

 the nuclear substance is the sole carrier of hereditary tenden- 

 cies : the view which I expressed ten years earlier (1873), of 

 the physiological equality (Homodynamy) of the nuclei of both 

 male and female germ-cells, became to my mind a certainty, 

 and I then advanced the theory of fertilization which is to be 

 found in my fourth essay. No one, as far as I know, w4th the 

 single exception of Strasburger, has expressed similar views 

 on the essential nature of fertilization, at any rate with regard 

 to the homodynamy of the sexual nuclei. The distinguished 

 observer E. van Beneden, to whom we owe so much of our 

 knowledge of the processes of fertilization, has maintained his 

 belief in the old view which looks upon fertilization as the union 

 of two elements which are essentially opposed to each other. 

 He is unable to free himself from the dominant idea, so firmly 

 embedded in the biological mind, that sexual difference is 

 something fundamental, and an essential principle of life itself. 

 To him, the fertilized ovum is a ' hermaphrodite ' being, which 

 unites in itself both male and female entities,— an idea which 

 has commended itself to man}^ authorities, but an idea of which 

 the logical outcome forces us to regard all the cells of the body 

 as hermaphrodite. Van Beneden was at the same time swayed 

 by the opinion, which is shared by so many workers in other 

 lands, that fertilization is a process of rejuvenescence, without 

 which terrestrial life could not continue. Many observers still 



