INTRODUCTION 5 



Liter through researches on the early history of the germ-cells and the 

 fertilization of the ovum. Begun in 1873-74 by Auerbach, Fol, and 

 Biitschli, and eagerly followed up by Oscar Hertwig, Van Beneden, 

 Strasbur^er, and a host of later workers, these investigations raised 

 wholly new questions regarding the mechanism of development and 

 the role of the cell in hereditary transmission. The identification of 

 the cell-nucleus as the vehicle of inheritance, made independently and 

 almost simultaneously in 1884-85 by Oscar Hertwig, Strasburger, 

 Kblliker, and Weismann, must be recognized as the first definite 

 advance 1 towards the internal problems of inheritance through the 

 cell-theory ; and the discussions to which it gave rise, in which Weis- 

 mann has taken the foremost place, must be reckoned as the most 

 interesting and significant of the post-Darwinian period. 



These discussions have set forth in strong relief the truth that 

 the general problems of evolution and heredity are indissolubly 

 bound up with those of cell-structure and cell-action. This can best 

 be appreciated from an historical point of view. The views of the 

 early embryologists in regard to inheritance were vitiated by their 

 acceptance of the Greek doctrine of the equivocal or spontaneous 

 generation of life ; and even Harvey did not escape this pitfall, near 

 as he came to the modern point of view. "The egg," he says, "is 

 the mid-passage or transition stage between parents and offspring, 

 between those who are, or were, and those who are about to be ; 

 it is the hinge or pivot upon which the whole generation of the 

 bird revolves. The egg is the terminus from which all fowls, male 

 and female, have sprung, and to which all their lives tend it is the 

 result which nature has proposed to herself in their being. And 

 thus it comes that individuals in procreating their like for the sake 

 of their species, endure forever. The egg, I say, is a period or por- 

 tion of this eternity." 2 



This passage appears at first sight to be a close approximation to 

 the modern doctrine of germinal continuity about which all theories 

 of heredity are revolving. To the modern student the germ is, in 

 Huxley's words, simply a detached living portion of the substance 

 of a pre-existing living body 3 carrying with it a definite structural 

 organization characteristic of the species. Harvey's view is only 

 superficially similar to this ; for, as Huxley pointed out, it was obscured 

 by his belief that the germ might arise "spontaneously," or through 



1 It must not be forgotten that Haeckel expressed the same view in 1866 only, how- 

 ever, as a speculation, since the data necessary to an inductive conclusion were not obtained 

 until long afterwards. "The internal nucleus provides for the transmission of hereditary 

 characters, the external plasma on the other hand for accommodation or adaptation to the 

 external world" (Gen. Morph., p. 287-9). 



-De Generation*, 1651; Trans., p. 271. 



3 Evolution in Biology, 1878; Science ami Culture, p. 291. 



