ON THE GENETIC VIEW OF NATUEE. 



307 



that which Haeckel has termed " Ontogenesis," the genesis 

 of the individual being. From this Haeckel distinguishes 

 " Phylogenesis," the genesis of the phyla, the genera, and 

 species. Now, in discussing the relation of the order 

 which prevails in the natural systems of animals to 

 the stages of development of individual embryos, von 

 Baer does not seem to have had before his mind the 

 genesis of one species out of another, a view which he 

 in fact ridicules l after a very modern fashion. He looked 



1 Loc. cit., p. 200 ; transl., p. 187 

 (1828) : "This idea viz., that the 

 higher forms of animals in the single 

 stages of the development of the in- 

 dividual, from its first origin to its 

 completed development, answer to 

 the permanent forms of the animal 

 series . . . could not fail to be 

 widely accepted, since it was sup- 

 ported by a multitude of special 

 demonstrations. Certain of its ad- 

 vocates were so zealous that they 

 no longer spoke of similarity but of 

 perfect identity, and assumed that 

 the correspondence had been de- 

 monstrated in all cases and to the 

 minutest details. . . . By degrees 

 it became the custom to look upon 

 the different forms of animals as 

 developed out of one another, and 

 then many appeared to forget that 

 this metamorphosis was after all 

 only a mode of conceiving the facts. 

 ... At length, in sober serious- 

 ness, and with all due particularity, 

 we were informed exactly how they 

 arose from one another. Nothing 

 could be easier. A fish, swimming 

 towards the shore, desires to take 

 a walk, but finds his fins useless. 

 They diminish in breadth for want 

 of use, and at the same time elon- 

 gate. This goes on with children 

 and grandchildren for a few myriads 

 of years, and at last, who can be 

 astonished that the fins become 



feet ? It is still more natural that 

 the fish in the meadow, finding no 

 water, should gape after air, there- 

 by, in a like period of time, develop- 

 ing lungs ; the only difficulty being 

 that in the meanwhile a few genera- 

 tions must manage to do without 

 breathing at all. The long neck of 

 the heron arose from a habit its 

 ancestors acquired of stretching out 

 their necks for the purpose of catch- 

 ing fish. . . . An immediate conse- 

 quence of the assumption of this 

 idea as a natural law was that a 

 view which had once been very 

 general, but had subsequently been 

 pretty generally given up, that of 

 the universal progression of the 

 different forms of animals, gradu- 

 ally got footing again. ... It 

 must be confessed that the natural 

 law being assumed, logical conse- 

 quence required the admission of 

 the view in question. There was 

 then only one road of metamor- 

 phosis, that of further develop- 

 ment, either attained in one in- 

 dividual (individual metamorphosis) 

 or through the different animal 

 forms (the metamorphosis of the 

 animal kingdom) ; and disease was 

 to be considered as a retrogressive 

 metamorphosis, because universal 

 metamorphosis, like a railroad, 

 allows motion backwards or for- 

 wards, but not to one side." 



