390 



SCIENCE 



[N. S. Vol. XXVIII. No. 717 



energy devoted to its improvement by its 

 distinguished author, Weismannism fails, 

 in my opinion, to be a satisfactory theory 

 of evolution. 



All such theories must account for two 

 things which are parts of a single process 

 but may logically be considered sepa- 

 rately: (1) The fact of ontogeny, namely, 

 that the ovum has the capacity of develop- 

 ing into a certain more or less predeter- 

 mined form; (2) the fact of heredity — 

 the circumstance that this form is ap- 

 proximately the same as that of the parent. 



The doctrine of pangenesis accounts for 

 heredity, since the germ-cells are imagined 

 as made up of gemmules representing all 

 parts of the adult ; but it does not account 

 for ontogeny, because there seems to me no 

 sufficient reason why the gemmules should 

 become active in a predetermined order 

 unless, indeed, we allow that they do so by 

 habit, and then the doctrine of pangenesis 

 becomes a variant of the mnemic theory. 



The strength of Weismann's theory lies 

 in its explanation of heredity. Accord- 

 ing to the doctrine of continuity, a frag- 

 ment of the germ-plasm is, as it were, put 

 on one side and saved up to make the 

 germ-cell of the new generation, so that 

 the germ-cells of two successive genera- 

 tions are made of the same material. 

 This again depends on Weismann's belief 

 that when the ovum divides, the two 

 daughter cells are not identical; that in 

 fact the fundamental difference between 

 soma and germ-cells begins at this point. 

 But this is precisely where many natural- 

 ists whose observations are w^orthy of all 

 respect differ from him. Weismann's 

 theory is therefore threatened at the very 

 foundation. 



Even if we allow Weismann's method 

 of providing for the identity between the 

 germ-cell of two successive generations, 

 there remains, as above indicated, a 

 greater problem— namely, that of ontog- 



eny. We no longer look at the potential- 

 ity of a germ-cell as Caliban looked on 

 Setebos, as something essentially incom- 

 prehensible, ruling the future in an un- 

 known way— "just choosing so." If the 

 modern germ-cell is to have a poetic ana- 

 logue it must be compared to a Pandora's 

 box of architectonic sprites which are let 

 loose in definite order, each serving as a 

 master builder for a prescribed stage of 

 ontogeny. Weismann's view of the mech- 

 anism by which his determinants— the 

 architectonic sprites — come into action in 

 due order is, I assume, satisfactory to 

 many, but I confess that I find it difficult 

 to grasp. The orderly distribution of 

 determinants depends primarily on their 

 arrangement in the ids, where they are 

 held together by "vital affinities." They 

 are guided to the cells on which they are 

 to act by differential divisions, in each of 

 which the determinants are sorted into 

 two unequal lots. They then become ac- 

 tive, i. e., break up into biophores, partly 

 under the influence of liberating stimuli 

 and partly by an automatic process. Pin- 

 ally the biophores communicate a "defi- 

 nite vital force" to the appropriate cells.' 

 This may be a description of what hap- 

 pens; but inasmuch as it fails to connect 

 the process of ontogeny with physiological 

 processes of which we have definite knowl- 

 edge, it does not to me seem a convincing 

 explanation. 



For myself I can only say that I am not 

 satisfied with Weismann's theory of hered- 

 ity or of ontogeny. As reg'ards the first, 

 I incline to deny the distinction between 

 germ and soma, to insist on the plain facts 

 that the soma is continuous with the germ- 

 cell, and that the somatic cells may have 

 the same reproductive qualities as the 

 germ-cells (as is proved by the facts of 

 regeneration) ; that, in fact, the germ-cell 



' " Tlie Evolution Theory," English translation, 

 I., 373 et seq. 



