178 THE CONTINUITY OF THE GERM-PLASM AS THE 



coalesce irregularly, but that their loops are placed regularly opposite 

 one another in pairs and thus form one new nucleus (the first seg- 

 mentation nucleus), distinctly pointed to the conclusion that the 

 nuclear substance is the sole bearer of hereditary tendencies that 

 in fact fertilization depends upon the coalescence of nuclei. Van 

 Beneden himself did not indeed arrive at these conclusions : he was 

 prepossessed with the idea that fertilization depends upon the union 

 of two sexually differentiated nuclei, or rather half-nuclei the male 

 and female pronuclei. He considered that only in this way could a 

 single complete nucleus be formed, a nucleus which must of course 

 be hermaphrodite, and he believed that the essential cause of further 

 development lies in the fact that, at each successive division of 

 nuclei and cells, this hermaphrodite nature of the nucleus is main- 

 tained by the longitudinal division of the loops of each mother- 

 nucleus, causing a uniform distribution of the male and female 

 loops in both daughter-nuclei. 



But van Beneden undoubtedly deserves great credit for having 

 constructed the foundation upon which a scientific theory of heredity 

 could be built. It was only necessary to replace the terms male 

 and female pronuclei, by the terms nuclear substance of the male 

 and female parents, in order to gain a starting-point from which 

 further advance became possible. This step was taken by Stras- 

 burger, who at the same time brought forward an instance in 

 which the nucleus only of the male germ-cell (to the exclusion of 

 its cell-body) reaches the egg-cell. He succeeded in explaining 

 the process of fertilization in Phanerogams, which had been for a 

 long time involved in obscurity, for he proved that the nucleus of 

 the sperm-cell (the pollen-tube) enters the embryo-sac and fuses 

 with the nucleus of the egg-cell : at the same time he came to 

 the conclusion that the body of the sperm-cell does not pass into 

 the embryo-sac, so that in this case fertilization can only depend 

 upon the fusion of nuclei l . 



1 Eduard Strasburger, ' Neue Uutersuchungen iiber den Befruchtungsvorgang bei 

 den Phanerogaraen als Grundlage fur eine Theorie der Zeugung.' Jena, 1884. 



[It is now generally admitted that, in the Vascular Cryptogams, as also in Mosses 

 and Liverworts, the bodies of the spermatozoids are formed by the nuclei of the cells 

 from which they arise. Only the cilia which they possess, and which obviously merely 

 serve as locomotive organs, are said to arise from the surrounding cytoplasm. It is 

 therefore in these plants also the nucleus of the male cell which effects the fertilization 

 of the ovum. See Gobel, 'Outlines of Classification and Special Morphology," trans- 



