yS Evolution and Adaptation 



an occasional accidental parallelism between the ontogeny 

 and the phylogeny which I deny, but the causal relation 

 between the two. Had the ancestors had larger antlers than 

 the existing ones, there is no justification for the assumption 

 that existing stags would acquire antlers of which each pair, 

 in later years, would be smaller than those of the previous 

 year." 



Hurst concludes : " There are many breeds of hornless 

 sheep, but they do not bear large horns in early years and 

 then shed them. If a rudiment ever appears in the embryo 

 of such sheep, its growth is very early arrested." The case 

 of the appendix in man might have been cited here as 

 a case in point. It is supposed to have been larger in the 

 ancestors of man, but we do not find it appearing full size in 

 the embryo and later becoming rudimentary. The preceding 

 statements will show that, while Hurst's view is similar in some 

 respects to my own, yet it differs in one fundamental respect 

 from it, and in this regard he approaches more nearly to the 

 theory of Von Baer. 



Hertwig has recently raised some new points of issue in 

 regard to the recapitulation theory, and since he may appear 

 to have penetrated farther than most other embryologists of 

 the present time, it will be necessary to examine his view- 

 somewhat carefully. He speaks of the germ-cell (egg, or 

 spermatozoon) as a species-cell, because it contains, in its 

 finer organization, the essential features of the species to 

 which it belongs. There are as many of these kinds of cells 

 as there are different kinds of animals and plants. Since the 

 bodies of the higher animals have developed from these 

 species-cells, so the latter must have passed in their phylogeny 

 through a corresponding development from a simple to a 

 more and more complex cell-structure. " Our doctrine is, 

 that the species-cell, even as the adult, many-celled representa- 

 tive of the species, has passed through a progressive, and, 

 indeed, in general a corresponding development in the course 



