172 NATURAL SCIENCE. ^,^^_ 



411); or (ii.) by combinations of distinct germ-plasms by sexuality 

 (pp. 293, 321, 327).^ 



I. The Continuity of Germ-plasm. 



The following quotations will express Dr. Weismann's views on 

 this point in his own words : — " A continuity of the germ-cells does 

 not now take place, except in very rare instances ; but this fact does 

 not prevent us from adopting a theory of the continuity of germ- 

 plasm'" (p. 173). " That continuity is maintained, by assuming that 

 a small part of the germ-plasm persists unchanged during the division 

 of the segmentation-nucleus, and remains mixed with the idioplasm of 

 a certain series of cells, and that the formation of true germ-cells is 

 brought about at a certain point in the series by the appearance of 

 cells in which the germ-plasm becomes predominant" (p. 197). This 

 "point " is, on the one hand, the nucleus or egg-cell of the embryo- 

 sac, and, on the other, the sperm-cell or fertilising nucleus of the 

 pollen-grain (p. 402); for "the nuclear substance must be the sole 

 bearer of hereditary tendencies" (p. 179). 



With regard to the mode of development of hereditary characters, 

 whether in the vegetative or reproductive organs of plants, he quotes 

 Strasburger, who says, " the nuclei determine the specific direction 

 in which an organism develops" (p. 185). "The nucleoplasm will 

 enter upon definite and varied changes which must cause the 

 differences appearing in the cells which are produced " (p. 185). " The 

 complexity of the molecular structure [of nucleoplasm] decreases as 

 the potentiality for further development also decreases " (p. 191) ; and 

 therefore, " it has lost the power of originating any new kind of cell " 

 (P- I95)' Therefore, " A sudden transformation of the nucleoplasm 

 of a somatic cell into that of a germ-cell would be almost as 

 incredible as the transformation of a mammal into an amoeba " 

 (p. 200). " There is no nucleoplasm like that of the germ-cell in 

 anj' of the somatic cells" (p. 195), excepting presumably the germ- 

 plasm contained in " the certain series of cells " (p. 197) by which its 

 continuity is maintained. 



Tlie above deductions were drawn from Dr. Weismann's study 

 of the Hydroids, on which he thus speaks : — " As a result of my 

 investigations on Hydroids, I concluded that the germ-plasm is pre- 

 sent in a very finely divided, and therefore invisible state in certain 

 somatic cells, from the very beginning of embryonic development, 

 and that it is transmitted through innumerable cell-generations to 

 those remote individuals of the colony in which sexual products are 



2 Dr. Weismann has also said elsewhere : — "A species is only caused to change 

 through the influence of changing external conditions of life, the change being in a 

 fixed direction. . . Transmutation by purely internal causes is not to be 



entertained. . . . The action of external inciting causes in the widest sense of 

 the word is alone able to produce modifications." Nature, vol. 22, p. 141. 



