INTRODUCTION y 



tance, made independently and almost simultaneously in 18S4-85 by 

 -Oscar Hertwig, Strasburger, Kolliker, and Wcismann/ while nearly 

 at the same time (1883) the splendid researches of Van Beneden on 

 the early history of the animal Qgg opened possibilities of research 

 into the finer details of cell-phenomena of which the early workers 

 could hardly have dreamed. 



We can only appreciate the full historical significance of the new 

 period thus inaugurated by a glance at the earlier history of opinion 

 regarding embryological development and inheritance. To the modern 

 student the germ is, in Huxley's words, simply a detached living por- 

 tion of the substance of a preexisting living body ^ carrying with it a 

 definite structural organization characteristic of the species. By the 

 earlier embryologists, however, the matter was very differently re- 

 garded ; for their views 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 Qgg,'' he savs, " 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 Qgg 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." ^ 



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

 the modern doctrine of s^erminal continuitv about which all theories 

 of heredity are revolving. In point of fact, however, Harvey's 

 view is only superficially similar to this doctrine ; for, as Huxley 

 pointed out, it was obscured by his belief that the germ might arise 

 *' spontaneously," or through the influence of a mysterious '' calidiun 

 innaUmi,'' out of not-living matter."* Neither could Harvey, great 

 physiologist and embryologist as he w^as, have had any adequate con- 

 ception of the real nature of the ^gg and its morphological relation to 



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 afterward. "The internal nucleus provides for the transmission of hereditary 

 characters, the external plasma on the other hand for accommodation i)« adaptation to the 

 external world" {Gen. MorpJi., pp. 2S7-289). 



2 Evolution in Biology, 1878; Science and Culture, p. 291. 

 ^ De Generatione, 1651; Trans., p. 271. 



^ Whitman, too, in a brilliant essay, has shown how far Harvey was from any real grasp 

 of the law of cenetic continuitv. which is well characterized as the central fact of modern 

 biology. Evolution and Epigenesis, Wood's HoU Biological Lectures, 1894. 



