THE LAW OF RECAPITULATION. 41 



contrary, do remain so capable, and it is precisely in order to preserve this capac- 

 ity that they hold aloof from the formation of the bodyt.issues and pursue their 

 own independent career. A portion of the germ-plasm of the parent ovum is, 

 so to speak, short-circuited into the genital elements which produce the offspring. 



If we accept this view, we are forced to make the supplementary hypothesis 

 that the conspicuous complicated changes, by which the germ-cells are converted 

 into sexual elements, do not involve the differentiation in the true sense — i. e., 

 strictly comparable to that which we observe in the somatic cells. Although 

 this hypothesis 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 conver- 

 sion into completely 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 ce'1-gemmules, or, as the cellular theory is not fully 

 established, simply gemmules. They are supposed to be transmitted from the 

 parents to the offspring, 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 according 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 Weismann's complicated useless hypotheses. All of these specu- 

 lations have only an historical interest, having proved themselves, from a scien- 

 tific standpoint, to be absolutely barren. 



The Law of Recapitulation. 



This law as commonly formulated, is that the development of the indi- 

 vidual recapitulates the development of the race, or, in other words, the ontogeny 

 recapitulates the phytogeny. This way of stating the law is in so far objectionable 

 that it presents the theoretical interpretation of the law rather than the actual 

 generalization 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 estab- 

 lished by Darwin this resemblance has been interpreted as due to the inheritance 



