In some of the tree snakes, notably _Passerita_, there is no appendage, but the long snout is itself endowed with mobility. This is a nocturnal snake; a harmless and exceedingly slender, graceful creature. [Illustration: Profile of _Passerita_.] But of these curious developments or prolongations, one of the Indian fresh-water snakes presents a remarkable example, almost allying it to some of the fishes with long tentacular appendages. _Herpeton tentaculum_ is its name, its pair of tentacles being scaly and flexible, and in appearance somewhat like the African viper’s horns, sticking out horizontally from its snout. They are employed under water as organs of touch, and probably to discern food. These are some of the most striking head-appendages; though in the way of pug-nosed ophidians and curious profiles we might give a whole page of illustrations. In the acrobatic chapter, mention was made of a pair of rudimentary hind limbs in some of the boas. Externally the derm is condensed into ‘claws’ or ‘hooks.’ In form they are merely long, simple appendages, which in the largest boas are about as big as a finger. Claws and hooks they are in the matter of use, being a pair, and they no doubt assist the climbing snakes in grasping. As a condensed form of the tegument, they are included in this chapter; but as they are truly vestiges of limbs, I will digress a moment to add a word. Says Darwin on rudimentary and atrophied limbs: ‘The disuse of parts leads to their reduced size: and the result is inherited.’ Some tame little lizards in my possession—our native species—when crawling about their cages scratching the sand or pushing their way among the moss and rubbish, frequently made use of their fore legs only, allowing the hind legs to drag after them, not because the latter were in any way injured, but simply because the lizards could do well enough without them. They were folded back or permitted to lie passively prone against the tail, while the arms and exquisite little hands were sufficient for the work required. They reminded one of Darwin’s words, and though my style of talking to my pets was such as to suit lizard comprehension solely, I did sometimes warn them in plain English. ‘If you don’t give your legs sufficient exercise, they will dwindle away by and by, and your descendants will have no hind legs at all!’