482 SCIENCE PROGRESS 



The conclusion drawn from such experiment is that there is 

 an early stage of embryonic development during which each 

 cell is pursuing the proper course predetermined by its own 

 inherited qualities ; and that to this there succeeds a stage in 

 which the interference of the general functional activity of the 

 organism is necessary to the completion of the process. In this 

 distinction we get the first glimpse of directness and indirectness 

 of inheritance. Characters determined by the first stage are 

 more directly dependent upon inheritance than those deter- 

 mined during the second. What evidence is there, then, that 

 the functional capabilities of cells are determined rather in the 

 direct than in the indirect stage of development ? On this point 

 the evidence is scanty. One can discover here and there an 

 isolated observation, such as that made by Wintrebert, for 

 example, that the muscle cells of the developing frog show 

 a capability of contraction in answer to mechanical stimuli at 

 a time when they are not yet in functional connection with 

 the central nervous system. Such observations as this suggest 

 that functional capability is in some cases at any rate deter- 

 mined at an early stage of development. There is no indi- 

 cation that it is a property the traces of whose phylogenetic 

 development will be easily wiped out. In this connexion the 

 importance of the distinction between functional capability and 

 functional behaviour becomes even more apparent. For the 

 latter, being dependent upon the activity of cells other than 

 those by which it is immediately exhibited, may well be open 

 to frequent adaptive modification determined by the environ- 

 ment of the organism ; while the former appears, from the 

 evidence quoted above, to be capable of establishment at a 

 period of development when such interference is not }^et 

 possible. 



We might carry this discussion on to the further point, 

 how far the use of functional capability might legitimately 

 be extended to the comparison of animals under the method 

 of homology, and how far it should be limited to the direct 

 method of comparison. But it is obvious that any conclusions 

 which might be reached in the present state of our knowledge 

 would rest upon such slender evidence that their value could 

 not be great. The one patent fact is that we know scarcely 

 anything at all about the functional capabilities of cells, whether 

 as regards development in the embryo or distribution through 



