132 TRANSITIONS OF ORGANIC BEINGS. [CHAP. VI. 



for us, whether habits generally change first and structure after- 

 wards ; or whether slight modifications of structure lead to changed 

 habits ; both probably often occurring almost simultaneously. 

 Of cases of changed habits it will suffice merely to allude to that 

 of the many British insects which now feed on exotic plants, or 

 exclusively on artificial substances. Of diversified habits innu- 

 merable instances could be given : I have often watched a tyrant 

 flycatcher (Saurophagus sulphuratus) in South America, hovering 

 over one spot and then proceeding to another, like a kestrel, and 

 at other times standing stationary on the margin of water, and 

 then dashing into it like a kingfisher at a fish. In our own 

 country the larger titmouse (Parus major) may be seen climbing 

 branches, almost like a creeper ; it sometimes, like a shrike, kills 

 small birds by blows on the head ; and I have many times seen 

 and heard it hammering the seeds of the yew on a branch, and 

 thus breaking them like a nuthatch. In North America the black 

 bear was seen by Hearne swimming for hours with widely open 

 mouth, thus catching, almost like a whale, insects in the water. 



As we sometimes see individuals following habits different from 

 those proper to their species and to the other species of the same 

 genus, we might expect that such individuals would occasionally 

 give rise to new species, having anomalous habits, and with their 

 structure either slightly or considerably modified from that of 

 their type. And such instances occur in nature. Can a more 

 striking instance of adaptation be given than that of a woodpecker 

 for climbing trees and seizing insects in the chinks of the bark ? 

 Yet in North America there are woodpeckers which feed largely 

 on fruit, and others with elongated wings which chase insects on 

 the wing. On the plains of La Plata, where hardly a tree grows, 

 there is a woodpecker (Colaptes campestris) which has tv,-o toes 

 before and two behind, a Jong pointed tongue, pointed tail- 

 feathers, sufficiently stiff to support the bird in a vertical position 

 on a post, but not so stiff as in the typical woodpeckers, and a 

 straight strong beak. The beak, however, is not so straight or so 

 strong as in the typical woodpeckers, but it is strong enough to 

 bore into wood. Hence this Colaptes in all the essential parts of 

 its structure is a woodpecker. Even in such trifling characters as 

 the colouring, the harsh tone of the voice, and undulatory flight, 

 its close blood-relationship to our common woodpecker is plainly 

 declared ; yet, as I can assert, not only from my own observations 

 but from those of the accurate Azara, in certain large districts it 

 does not climb trees, and it makes its nest in holes in banks ! In 

 certain other districts, however, this same woodpecker, as Mr. 

 Hudson states, frequents trees, and bores holes in the trunk for 

 its nest. I may mention as another illustration of the varied 

 habits of this genus, that a Mexican Colaptes has been described 



