In form it is not unsymmetrical, and in substance it is horny, like hair, nails, quills, and hardened skin, a sort of dense and corneous integument, yet less solid than horns and claws. The links, being only interlocked and yet elastic, can be easily separated, and are consequently easily injured. An animal treading on the rattle of a snake would cause a portion at least to be lost; or in being drawn among roots and entangled vegetation, a rattle might easily get damaged: the number of links can never, therefore, be an infallible clue to the age of the reptile. Like hair, horns, nails, it is also subject to a caprice in growth, or to the vigour of the individual; at one time comparatively at a stand-still, at another growing rapidly; in one season gaining perhaps several links, in another season none. Neither does the number of joints bear any relation to the casting of the skin, any more than the growth of hair or nails depends on the healing of a scar. The slough, cast more or less frequently, may leave the rattle intact, or a new link may appear at such a time. Dr. Cotton, of Tennessee, had a rattlesnake which shed its skin on an average twice a year, and he observed a new link to the rattle on each shedding. On the contrary, a rattlesnake at the London Zoological Gardens, and in the collection for about ten years, had never a rattle worth mentioning. Quite a young snake of only 15 inches when brought, it grew into a fine healthy specimen, fully five feet long, and yet had never more than what Americans call the button—not quite even that, but merely an abortive pretence of unhealthy growth, as if one or two links were consolidated. I watched that rattle for several years with much interest. Thus it was when my attention was first drawn towards it; and though it sometimes gave promise of growing, and once did indeed gain another link, it soon got broken off, and never attained more than three misshapen joints. [Illustration: All there was of it! From life.] Though no rattle is ordinarily developed until the snakeling is some months old, several cases are on record where young snakes have been born with the ‘button,’ and even with perfectly formed links. Mr. Benjamin Smith Barton, an American who wrote a good deal about the Crotalus, communicated to Prof. Zimmermann in 1800 that he had found in a parent some young ones with three rattles, _i.e._ ‘links,’ each. Similar and more recent cases are on record. [Illustration: Transparent rattle (p. 296), held against the light.]