IV.] FOUNDATION OF A THEORY OF HEREDITY. l8l 



at each successive division of nuclei and cells, this herma- 

 phrodite nature of the nucleus is maintained 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 Strasburger, 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 ^ 



Thus the nuclear substance must be the sole bearer of 

 hereditary tendencies, and the facts ascertained by van 

 Beneden in the case oi A scar is plainly show that the nuclear 

 substance must not only contain the tendencies of growth of 

 the parents, but also those of a very large number of ancestors. 

 Each of the two nuclei which unite in fertilization must contain 

 the germ-nucleoplasm of both parents, and this latter nucleo- 



^ Eduard Strasburger, ' Neue Untersuchungen iiber den Befruch- 

 tungsvorgang bei den Phanerogamen als Grundlage fiir cine Theorie der 

 Zeugung.' Jena., 1884. 



[It is now generall}' 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 c^'toplasm. It is therefore 

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

 fertilization of the ovum. See Gdbel, ' Outlines of Classification and 

 Special Morphology,' translated by H. E. F. Garnsey, edited by I. B. 

 Balfour, Oxford, 1887, p. 203, and Douglas H. Campbell. ' Zur Entwick- 

 lungsgeschichte der Spermatozoiden,' in Berichte d. deutschen bot. 

 Gesellschaft, vol. v (1887), p. 120. — S. S.] 



