44 An Attempt to classify 



appears only to exert a secondary influence. The Iceland 

 breed of sheep, which feeds on the nutritious lichens of that 

 island, is of large size; and, like the other ruminant animals 

 which subsist on similar food, is remarkable for an extraor- 

 dinary developement of horns. Another example of acquired 

 variation^ dependent solely on the supply of nutriment, may 

 be observed in the deciduous horns of the deer family, which 

 are well known to be large or small according to the quality 

 of their food. That temperature also does exert an influence 

 greater or less, according to the species of animal, is very 

 evidently shown iu the case of the donkey *, of which there are 

 no breeds, nor true varieties, and but very few simple varia- 

 tions [VII. 590.] : this animal is every where found large or 

 small, according to the climate it inhabits. 



The influence of particular sorts of food may be exemplified 

 by the well-known property of madder (i?ubia tinctorum), 

 which colours the secretions, and tinges even the bones of the 

 animals which feed on it of a blood-red colour; and, as an- 

 other familiar instance, may be cited the fact, equally well 

 known, of bullfinches, and one or two other small birds, 

 becoming wholly black when fed entirely on hempseed. I 

 have known, however, this change to take place in a bird (the 

 small aberdevatt finch, so common in the shops), which had 

 been wholly fed on canary seed ; yet this by no means inva- 

 lidates the fact, so often observed, of its being very frequently 

 brought about by the direct influence of the former diet. In 

 several instances which have fallen under my own observation, 

 feeding only on hempseed has invariably superinduced the 

 change.f 



The most remarkable of acquired variations are those 

 brought about in animals in a state of confinement or domes- 

 tication : in which case an animal is supplied regularly with 

 abundance of very nutritious, though often unnatural, food, 

 without the trouble and exertion of having to seek for it, and 

 it becomes, in consequence, bulky and iazjr, and in a few 

 generations often very large; while the muscles of the organs 

 of locomotion, from being but little called into action, be- 

 come rigid and comparatively powerless, or are not developed 

 to their full size. The common domestic breeds of the 

 rabbit, ferret, guinea-pig, turkey, goose, and duck, are thus 

 probably only acquired variations, which, from the causes 



* For some curipus remarks on this subject, see the excellent article 

 " Ass " in Partington's Cyclojxzdia of Natural History. 



f I have not heard, however, that wild bullfinches, hawfinches, and other 

 birds liable to be thus affected, are more commonly found black in localities 

 where hemp is much grown. Amongst others, the skylark and woodlark 

 are very susceptible of the influence of this food. 



