B30 



SNAKES 



arrangements the j>oison-gland is automatically 

 compressed when the snake u|>eii8 its mouth to 

 trike. Hat the opening of the mouth ul-n 

 brings about the erection of the fangs, which are 



Fig. 1. 



Open mouth of a vrnnmoiu nnnke, ihiiwini: the fang* half-hidden 

 in their theatlu. (After Niihn.) 



recumbent and cnsheathed when not in use. Behind 

 each functional fang is a aeries of reserve fanga, 

 and if a fang be broken the foremost of the reserves 

 i- -hnnti-d forward, and liecoming fixed to the 

 maxilla replaces the one which has been lost 



The juice formed in the specialised glands 

 and forced out along the fangs is a clear viscid 

 fluid with an acid reaction, and with poison- 

 ous properties which vary according to the species 



Fig. 2. 



Dtaeetlon showing the poison-gland, a; lUduct, 6; the tubular 

 lung, r, il; the reserve fangs, . (After Nuhn.) 



and also with the vigour of the snake. It may be 

 kept for months or even years without losing its 

 virulence. Injected through the fangs into the Wood 

 of a victim, it tends to paralyse the nerve-centres. 

 It has most effect on birds and mammals, less on 

 cold-blooded animals, such as fishes. An injection 

 of the blood of a venomous snake may also prove 

 fatal. Several venomous snakes are unaffected by 

 their own venom, and Fayrer states that Cobras 

 and Dalmias may bite one another with impunity. 

 Mi' also notices that the 'sweepers and Diiomes ' 

 who attended hi* elaborate, experiments in India 

 were wont to eat the animals which had Keen 

 fatally bitten. In 1843 Lucien Bonaparte dis- 

 covered in the ]>ion of the adder (Pclias bents) 

 a substance which he called ' viperine,' but this 

 seems practically identical with the ptyaline of 

 ordinary saliva, and we are still far froin under- 

 standing why the juice of the poison-gland should 

 have itx peculiar properties. 



Food. Snakes are almost always carnivorous; 

 and, as is suggested by the nature of their teeth, 

 which are not adapted fur mastication, they swallow 

 llicir lxoty intact. Mammals, l>inls, reptiles, am- 

 phibians, fishes, molluscs, ami insect* are all eaten 

 by snake-, and there are many forms with strange 

 preference!* e.g. for milk and eggs. In the egg- 

 eating African snake Kacliiodon the teeth are 

 rudimentary. l>ut the inferior spines of the anterior 

 vertebne project on the dorsal wall of the gullet 

 and break the egg-shells. In many rases the prey 

 is relatively large larger indeed than the normal 

 ize of the month ami millet and the process of 

 wallowing is tedious. In the python, for instance, 

 there is a slow qontinnons action of jaws and teeth; 

 the victim is firmly held l.y one side of the mouth 

 while the other side U protruded and its teeth im- 

 planted further forward, and so on alternately on 



each side. Meanwhile the mobile bones of the 

 skull are lieing stretched to the utmost, and the 

 victim is covered with saliva which makes the 

 passage down the elastic gullet somewhat easier. 

 Alter a heavy meal the snake often lies dormant 

 for a time, after which it may cast its slough. 



Movement*. Owen has said of snakes that they 

 can 'outclimb the monkey, outawim the fish, out- 

 leap the zebra, outwrestle the athlete, and crush 

 the tiger;' yet all without limbs. The muscular 

 system is very strongly developed, and the long 

 ribs associated with most of the vertebrae serve 

 instead of legs. The serpent ' literally rows on the 

 earth, with every scale for an oar ; it bites the 

 dust with the ridges of its body.' On a very 

 smooth surface on glass, for instance it can 

 make no headway, but in normal conditions the 

 edges of the anterior ventral scales are fixed 

 against the roughnesses of the ground, the ribs are 

 drawn together first on one side then on the other, 

 the body is thus wriggled forward to the place of 

 attachment, the hind part fixes itself, the front part 

 shoots out, an anterior attachment is again effected, 

 and thus the snake glides on wards. Hut thisscaicely 

 suggests the swiftness or the beauty of what Kiiskin 

 calls 'one soundless, causeless march of sequent 

 rings, and spectral procession of spotted dust, with 

 dissolution in its fangs, dislocation in its coils. 

 Startle it ; the winding stream will become a 

 twisted arrow ; the wave of poisoned life will lasli 

 through the grass like a cost lance.' Were it not 

 for many fanciful pictures it would scarcely be 

 necessary to say that without any support snakes 

 are not able to raise the anterior part of their body 

 more than a short distance from the ground. 



Sloughing. It is well known that a snake 

 periodically 'caste ite skin,' leaving behind it a 

 continuous 'slough.' The same process occurs in 

 lizards, and to a less extent in some other animals. 

 What ia cast is the external layer of the epidermis, 

 and its continuity depends on the fact that the 

 scales are simply folds of skin. As to the pin Bi- 

 ology of the process, although a complete explana- 

 tion has not yet been given, it is evident that 

 the outer layer of the skin tends to die away, and 

 that the continued growth of the animal makes 

 sloughing necessary. The number of sloughings in 

 a year varies with the species of snake and also 

 with the age and health of the individual. Cobras 

 have been observed to slongh as often as once a 

 month, but this seems to be unusually often. 

 liefore sloughing snakes are often almost blinded 

 by the change in the skin over the eyes, and at 

 this time they are said to be very irritable. In 

 getting rid of its slouch the snake gets its head 

 free first, and the outer layer is turned inside out 

 from before backwards. 



Reproduction. The sexes are almost always 

 quite like one another externally, save that the 

 females are always larger. The internal organs of 

 reproduction are paired, but those of the right side 

 are often the larger and lie in front of those on the 

 left. The male has a double copulatory organ, some- 

 times covered with spines or hooks. The eggs, ferti- 

 lised within the oviducts, are more or less oblong in 

 shape, and are surrounded by a leathery envelope, 

 1 for the rupture of which the embryos are provided 

 with an egg-tooth, a special development like that 

 of the chick.' Most snakes are oviparous, but, as 

 among lizards, viviparous forms occur, such as the 

 British Adder (Pflinnor Vi/nr lirrux). It is said 

 that (IcoU'roy Saint-Hilaire and Flnrent I'revost 

 'succeeded in making the (normally oviparous) 

 Common Grass Snake viviparous by depriving it of 

 water and maintaining a suitable surrounding tern- 

 pcra i M n- ; ' and it may be that some viperine snakes 

 and the Boa Constrictor, which have borne their 

 young alive in captivity, are oviparous in natural 



