254 MENTAL EVOLUTION IN ANIMALS. 



moreover their extremely long toes seem admirably adapted 

 to walk over the softest swamps and floating plants ; yet the 

 common corncrake belongs to one of these very genera, and 

 having the same structure of feet, haunts meadows, and is 

 scarcely more aquatic than a quail or partridge." 



Tlie MS goes on to detail other and analogous cases, such 

 as that of the Ground-woodpecker, Ground-parrots, and 

 Tree-frogs, which have abandoned their arboreal habits ; in 

 all which cases the generic structures specially adapted to 

 arboreal habits remain. Similarly the swallow-tailed Hawk 

 is mentioned as catching flies on the wing like a swallow ; 

 a Petrel — " those more aerial of birds " — which has assumed 

 the habits of an Auk; the Water-ouzel, a member of the 

 Thrush family, which runs along the bottom of streams 

 usino" its wings for diving and its feet for grasping stones 

 under the water, " and yet the keenest observer could never 

 have foretold this singular manner of life from the most 

 careful examination of its structure." 



All the above cases are given by Mr. Darwin, not in re- 

 lation to Instinct, but to enforce his argument on adaptive 

 structures being developed by natural selection instead of 

 designed in special creation. But I have used them in 

 relation to the development of Instinct, because, if we already 

 believe in the natural evolution of organic structures, such 

 cases as these afford the best possible evidence of the varia- 

 tion of instinct. As evolutionists we could have no stronger 

 testimony to the previous though now obsolete instincts of a 

 species, than that which is supplied by the presence of pecu- 

 liar though useless structures which in allied species are 

 correlated with particular instincts. For we must always re- 

 member, as previously observed, that instincts are never, like 

 structures, fossilized, and therefore that we can never obtain 

 direct historical evidence of their transmutation. But the 

 best substitute for this evidence is, I think, such testimony 

 as I have adduced of persisting structures pointing to obsolete 

 instincts. Similar evidence in kind, though not quite so 

 strong in degree, is furnished by cases in which one species 

 of a genus, or one genus in a family, exhibits an instinct 

 peculiar to that species or genus — i.e., cases in which the 

 instinct does not occur in allied species and genera ; for this 

 shows, if w^e already accept the doctrine of the transmutation 

 of species, that the peculiar instinct must have arisen in the 



