388 PROVISIONAL HYPOTHESIS Chap. XXVII. 



such as an additional limb or an antenna, springs from a false 

 position, it is only necessary that the few first gemmules 

 should be wrongly attached ; for these whilst developing 

 would attract other gemmules in due succession, as in the 

 re-growth of an amputated limb. When parts which are 

 homologous and similar in structure, as the vertebra? of 

 snakes or the stamens of pobyandrous flowers, &e, are re- 

 peated many times in the same organism, closely allied 

 gemmules must be extremely numerous, as well as the points 

 to which they ought to become united ; and, in accordance 

 with the foregoing views, we can to a certain extent under 

 stand Isid. Geoffroy Saint-Hilaire's law, that parts, which are 

 already multiple, are extremely liable to vary in number. 



Variability often depends, as I have attempted to show, 

 on the reproductive organs being injuriously affected by 

 changed conditions ; and in this case the gemmules derived 

 from the various parts of the body are probably aggregated 

 in an irregular manner, some superfluous and others deficient. 

 Whether a superabundance of gemmules would lead to the 

 increased size of any part cannot be told ; but we can see 

 that their partial deficiency, without necessarily leading to 

 the entire abortion of the part, might cause considerable 

 modifications ; for in the same manner as plants, if their own 

 pollen be excluded, are easily hyhridised, so, in the case of 

 cells, if the properly succeeding gemmules were absent, 

 they would probably combine easily with other and allied 

 gemmules, as we have just seen with transposed parts. 



In variations caused by the direct action of changed con- 

 ditions, of which several instances have been given, certain 

 parts of the body are directly affected by the new conditions, 

 and consequently throw off modified gemmules, which are 

 transmitted to the offspring. On any ordinary view it is 

 unintelligible how changed conditions, whether acting on the 

 embryo, the young or the adult, can cause inherited modifica- 

 tions. It is equally or even more unintelligible on any 

 ordinary view, how the effects of the long-continued use or 

 disuse of a part, or of changed habits of body or mind, can be 

 inherited. A more perplexing problem can hardly be pro- 



