CuAP. I. U^'DER DOMESTICATION. 03 



rcctly ou the -wliole orn-anizalion or on certain parts alone, and 

 indirectly by affecting the reproductive system. With respect 

 to the direct action, Ave must bear in mind that in every case, 

 as Prof. Weismann has lately insisted, and as I have incident- 

 ally shown in my -work on " Variation under Domestication," 

 there are two factors : namely, the nature of the organism, and 

 the nature of the conditions. The former seems to be much 

 the more important; for nearly similar variations sometimes 

 arise under, as far as we can judge, dissimilar conditions ; and, 

 on the other hand, dissimilar variations under conditions which 

 appear to be nearly uniform. The effects on the offspring are 

 cither defmite or indefmitc. They may be considered as defi- 

 nite when all or nearly all the offspring of individuals exposed 

 to certain conditions during several generations are modified 

 in the same manner. It is extremely difficult to come to any 

 conclusion in rcgjird to the extent of the changes which have 

 been thus definitely induced. There can, however, be little 

 doubt about many slight changes — such as size from the 

 amoimt of food, color from the nature of the food, thickness of 

 the skin and hair from climate, etc. Each of the endless vari- 

 ations which we sec in the plumage of our fowls must hare 

 had some efficient cause ; and if the same cause were to act 

 uniformly during a long scries of generations on many indi- 

 viduals, all probably would be modified in the same manner. 

 Such facts as the complex and extraordinary outgrowths 

 which invariably follow from the insertion of a minute drop of 

 ])oison by a gall-producing insect, show us what singular mod- 

 ifications might result in the case of plants from a chemical 

 change in the nature of the sap. 



Indefinite variability is a much more common result of 

 changed conditions than definite variability, and has probably 

 played a more important part in the formation of our domestic 

 races. We see indefinite Aariability in the endless slight pe- 

 culiarities which distinguish the individuals of the same spe- 

 cies, and which cannot be accounted for by inheritance from 

 cither parent or from some more remote ancestor. Even 

 strongly-marked differences occasionally appear in the young 

 of the same litter, and in seedlings from the same seed-capsules. 

 At long intervals of time, out of millions of individuals rc^ared 

 in the same country and fed on nearly the same fooJ, dona- 

 tions of structure so strongly pronounced as to deserve to be 

 called monstrosities arise; but monstrosities cannot be sepa- 

 rated by any distinct Une from slighter variations. All such 



