THE LAW OF RECAPITULATION. 29 



sis seems a logical necessity of the theory of germinal continuity, we cannot at 

 present verify it by any observed facts. 



The only other theory of heredity which has ever been seriously considered is 

 that of pangenesis, which was formulated by Darwin, whose words I quote: "But 

 besides this means of increase I assume that cells before their conversion into com- 

 pletely passive or 'form-material' throw off minute granules or atoms, which 

 circulate freely throughout the system, and when supplied with proper nutriment 

 multiply by self-division, subsequently becoming developed into cells, like those from 

 which they were derived. These granules, for the sake of distinctness, may be 

 called cell-gemmules, or as the cellular theory is not fully established, simply 

 gemmules. They are supposed to be transmitted from the parents to the off- 

 spring, and are generally developed in the generation which immediately succeeds, 

 but are often transmitted in a dormant state during many generations, and are 

 then developed." 



Many modifications of this theory have been proposed by speculative writers, 

 and many different names have been bestowed upon the gemmules of Darwin ac- 

 cording to the fancy of each author and the particular set of qualities which he 

 attributed to these imaginary particles. Such views attained their culmination in 

 the set of elaborate and complicated hypotheses forming the doctrine of Weismann, 

 or so-called Weismannism, which was for a time widely and actively discussed. All 

 of these speculations have only an historical interest, having proved themselves, 

 from a scientific standpoint, to be absolutely barren. 



The Law of Recapitulation. 



This law, as commonly formulated, is that the development of the individual 

 recapitulates the development of the race, or, in other words, the ontogeny recapit- 

 ulates the phylogeny. This way of stating the law is in so far objectionable that it 

 presents the theoretical interpretation of the law rather than the actual generaliza- 

 tion of the facts. The essential datum upon which the law is based is, that the 

 embryo of a given animal has striking morphological resemblances to the adult 

 forms of lower allied types. Since the theory of evolution was established by Dar- 

 win this resemblance has been interpreted as due to the inheritance of ancestral 

 characters appearing in the embryo. The embryo is looked upon as the representa- 

 tive of the actual ancestor by modification of which the adult form was evolved. 

 It is further assumed that the change of the embryo into the adult type follows the 

 same general course as the development of the remote ancestor into the particular 

 species under consideration. Speaking broadly, this interpretation is undoubtedly 

 justifiable. If it were exactly true, it would be necessary only to know the em- 

 bryology of an animal in order to establish the evolution of the species. Experience, 

 however, very quickly demonstrates that this procedure is by no means possible, 

 because the embryo is not a correct or adequate record of the ancestral type. It is 

 inadequate chiefly for three reasons: first, because the embryo has necessities of its 



