630 H. S. Jennings 



it is not thrown off by regulation. If new inherited characters of 

 any sort are ever produced by environmental action, such direct 

 transmission of an acquired internal modification must occur, as 

 we have already seen (paragraph 11). In the Metazoa, it would 

 evidently be only general changes in the gernj cells that would be 

 thus directly transmitted. 



b The case of a new localized modification or of a definite new 

 structure, such as a spine, which is directly produced by environ- 

 mental action, is wholly different. As we have already seen (para- 

 graphs 9, 10, 11), in order that a new localized structure b shall 

 appear in each generation, a certain other condition a must be 

 produced in the mother cells; this condition a must be transmitted 

 from generation to generation, and must so modify the reproductive 

 processes as to cause, at each fission, the production of the new 

 structure b. 



Now, if the new structure b was first produced directly in the 

 parent by environmental action, and is then to be inherited, the 

 processes required are the following. The existence of the struc- 

 ture 7) (a spine, for example), in the parent cell, must cause the 

 production in that parent cell of precisely the "other" condition 

 a, that is of such a nature as to so change the processes of repro- 

 duction that they will again produce identically the character b 

 (the spine) which had first been produced by the environment. 

 Or, what amounts to practically the same thing, the environment 

 must coincidentally produce two heterogeneous effects: (i) it 

 must directly produce the structure b; (2) it must produce some 

 permanent change a in the constitution of the cell, such as will so 

 modify the processes of reproduction that they in their turn will 

 produce the same structure b. 



Such coincidental production of a complex structure b in two 

 quite heterogeneous ways would be most extraordinary, and we 

 have as yet no glimmering of a mechanism by which the coinci- 

 dence could be produced. Moreover, as we have seen, in most 

 cases (in all precisely observed cases) it is not produced; we have 

 little if any direct evidence that it ever occurs. 



Yet if it ever occurred it would be of such importance that we 

 must of course continue to be on the watch, in all experimental 



