Page:The Works of William Harvey (part 1 of 2).djvu/524

 needful to the being or to the maintenance of the individual, but only as defences against external injury, as ornaments, or as weapons of offence.

The outermost part -of all, the skin, with its several append- ages, cuticle, hair, wool, feathers, scales, shells, claws, hooves, and other items of the same description, may be regarded as the principal means of defence or protection. And it is well devised by nature, who, indeed, never does aught amiss, that these parts are the last to be engendered, inasmuch as they could never be of use or avail as defences until the animal was born. The common domestic pullet is therefore born covered with down only, not with feathers, like certain other birds which have to be speedily prepared for flight, because it has to seek its food on foot, not on the wing, and by active running about hither and thither. In like manner the young of ducks and geese, which feed swimming, have their feathers and wings perfected at a later period than their feet and legs. It is otherwise with swallows, however, which have to fly sooner than to walk, be- cause they feed on the wing.

The down of the pullet begins to appear after the fourteenth day, the foetus being already perfect in all its parts. When the feathers first show themselves, they are in the guise of points within the skin, but by and by the feathers project, like plants from the ground, increase in length, become unfolded, invest the whole body, and protect it against the inclemencies of the atmosphere.

Feathers differ from quills in form, use, place of growth, and order of production. The pullet is feathered before it has any quills, for the quill-feathers only grow in the wings and tail, and also spring more deeply, from the very lowest part of the integument, or even from the periosteum, and serve essentially as instruments of motion ; the feathers again arise superficially from the skin, and are everywhere present as means of protection.

" Nails, hair, horn, and the like," says Aristotle, 1 " are en- gendered from the skin ; whence it happens that they change colour with the skin ; for the white and black and particoloured are so in consequence of the colour of the skin whence they

1 De Gener. Anim. lib. ii, cap. 1.