ON HEREDITY. 99 



wonderful indeed if the seeds were not also larger and better furnished 

 with nutritive material. If the increased nourishment be repeated 

 in the next generation, a still further increase in the size of the 

 seed, in the luxuriance of the plant, and in all other changes which 

 ensue, is at any rate conceivable if it is not a necessity. But this 

 would not be an instance of the transmission of acquired characters, 

 but only the consequence of a direct influence upon the germ-cells, 

 and of better nourishment during growth. 



A similar interpretation explains the converse change. When x 

 horses of normal size are introduced into the Falkland Islands, 

 the next generation is smaller in consequence of poor nourishment 

 and the damp climate, and after a few generations they have de- 

 teriorated to a marked extent. In such a case we have only to 

 assume that the climate which is unfavourable and the nutriment 

 which is insufficient for horses, affect not only the animal as a 

 whole, but also its germ-cells. This would result in the diminution 

 in size of the germ-cells, the effects upon, the offspring being still 

 further intensified by the insufficient nourishment supplied during 

 growth. 'But such results would not depend upon the transmission 

 by the germ-cells of certain peculiarities due to the unfavourable 

 climate, which only appear in the full-grown horse. 



It must be admitted that there are cases, such as the climatic 

 varieties of certain butterflies, which raise some difficulties against 

 this explanation. I myself, some years ago, experimentally investi- 

 gated one such case 1 , and even now I cannot explain the facts 

 otherwise than by supposing the passive acquisition of characters 

 produced by the direct influence of climate. 



It must be remembered, however, that my experiments, which 

 have been repeated upon several American species by H. W. 

 Edwards, with results confirmatory of my own in all essential 

 respects, were not undertaken with the object of investigating the 

 question from this point of view alone. New experiments, under 

 varying conditions, will be necessary to afford the true explana- 

 tion of this aspect of the question ; and I have already begun to 

 undertake them. 



Leaving on one side, for the moment, these doubtful, and 



1 ' Studien zur Descendenztheorie, I. Ueber den Saison-Dirnorphismus der 

 Schmetterlinge.' Leipzig, 1875. English edition translated and edited by Professor 

 Meldola, ' Studies in the Theory of Descent,' Part I. 



H 2, 



