In cold and temperate climates snakes hibernate, lying more or less torpid in holes or hollow trees, sometimes assembled in numbers and coiled together in a mass. The first thing they do in awakening in the spring is to cast the outer coating of the epidermis, as described above (p. 20). Several exuviations take place during the period of activity, sometimes pretty regularly every month, sometimes at very irregular intervals. A few days previous to this operation the snake is languid and abstains from feeding; its skin is dull and the sight impaired by the opaque condition of the lid; a day or two before moulting, the outer stratum of the epidermis becomes again transparent and the eye clear, through this stratum becoming detached from the subjacent tissue, until it is pulled off in one piece, by the snake rubbing itself against stones or bushes. The first exuviation takes place very shortly after birth. Snakes are long-lived, although the limit of duration of life is not known in any of them. They grow slowly, and do not appear ever to reach sexual maturity until the fourth year, when they continue increasing in size for a long period. A _Python reticulatus_ and an _Ancistrodon piscivorus_ are reported to have lived twenty-one years in captivity in Paris. The young of many snakes are very secretive, and are not often found in the open, those that are met with being as a rule either new-born or approaching sexual maturity. Snakes are tenacious of life, and remarkable for the reflex movements which take place after they have been cut to pieces, the severed parts of the body and tail wriggling for a considerable time, and the head endeavouring to bite. Accounts of decapitated Rattlesnakes turning round and striking with their bloody stumps are probably not snake stories. ------------------------------------------------------------------------ CHAPTER XI PARASITES Like all other animals, snakes are infested with a multitude of vegetable and animal parasites, both external and internal. About 300 species of Ophidian parasites have been recorded; yet our knowledge of them is very imperfect. Although some 2,000 species of snakes are known, parasites have not been recorded for more than 168 species, and in the great majority of these (102) only a single parasite: a tick, a hæmogregarine, or some intestinal worm. Owing to the more frequent opportunity of dissecting them, the common menagerie snakes have yielded better records, notwithstanding the fact that they usually lose most of their parasites through constant handling, prolonged fasting, and artificial surroundings. Thus, we have a list of thirteen species for the Indian _Python molurus_, and one of twenty-two species for the _Boa constrictor_. But no systematic search appears to have been attempted, save, perhaps, in the case of a few European species.