446 Dr. V. Fatio on the Variability/ of the 



the firm ground, the legs, naturally, do not follow the beak in 

 the necessity of elongation. It would be easy also to cite 

 other examples already indicated among the Mammalia, espe- 

 cially in certain races of cattle ; but we will not go beyond 

 our self-imposed limits. 



My business is only to demonstrate that the general laws of 

 adaptation which presided over the formation of types, continue 

 always to exercise their influence upon all individuals in 

 different conditions'^. 



Moreover I think that, in such investigations, we must not 

 seek too far for our points of comparison ; for, with its purpose 

 and its organization, each type also appears to have its own 

 tendencies to variability, may be as a predominant direction 

 for the possible modifications in a certain medium. In other 

 words, each species , or each group of allied forms, appears to 

 me, in our country and under certain conditions, to vary 

 preferently towards such or such a given point. The parts 

 more easily influencible constitute for the species at once the 

 weak point from the side of classification, and the strong point 

 as regards facility of adaptation, force of resistance, and power 

 of extension. 



It is evident that, according to the nature of the persistent 

 exigencies of the medium, it will be sometimes one and 

 sometimes another of the organs of relation that will be first 

 called upon to become modified ; but it is no less true that 

 in each species we shall always find, in a given medium, a par- 

 ticular character which is more subject to vary or more prompt 

 to become modified. The exact determination of the character 

 which, being the first modified, has reacted upon all the 

 others, has always appeared to Darwin excessively difficult ; and 

 yet it is upon the study of the variable preponderance of the 



* The history of our globe, painfully elaborated by geology and palae- 

 ontology, seems to be more and more in accord with zoology and physi- 

 ology upon this point. After leading us, in the forms of organisms, 

 through a whole series of successive modifications corresponding to the 

 different geological epochs and the different exigencies of the media of 

 the latter, palaeontology has shown ns, in fact, how, in sequence of a 

 change of stratum and of conditions of existence, many forms have often 

 disappeared, whilst some only continued to exist. In consequence, per- 

 haps, of a too rapid transformation of the conditions of life, those only 

 have been able to subsist which were sufficiently prepared or modified to 

 be able to sustain a rupture of equilibrium fatal to many others. Although 

 we cannot always so easily understand the sudden appearance in a new 

 stratum of an entirely- different fauna, I do not doubt, in common with 

 some authors, that by gradually piercing the obscurity which necessarily 

 envelops the variability of creatures long since lost, we shall succeed in 

 explaining these apparently sudden and complete changes without having 

 recourse to the necessity of a new creative intervention. 



