as is undoubtedly the case with our so…called _goose…skin_ before a fever…fit。 Animals have been repeatedly excited by rage and terror during many generations； and consequently the direct effects of the disturbed nervous system on the dermal appendages will almost certainly have been increased through habit and through the tendency of nerve…force to pass readily along accustomed channels。 We shall find this view of the force of habit strikingly confirmed in a future chapter； where it will be shown that the hair of the insane is affected in an extraordinary manner； owing to their repeated accesses of fury and terror。 As soon as with animals the power of erection had thus been strengthened or increased； they must often have seen the hairs or feathers erected in rival and enraged males； and the bulk of their bodies thus increased。 In this case it appears possible that they might have wished to make themselves appear larger and more terrible to their enemies； by voluntarily assuming a threatening attitude and uttering harsh cries； such attitudes and utterances after a time becoming through habit instinctive。 In this manner actions performed by the contraction of voluntary muscles might have been combined for the same special purpose with those effected by involuntary muscles。 It is even possible that animals； when excited and dimly conscious of some change in the state of their hair； might act on it by repeated exertions of their attention and will； for we have reason to believe that the will is able to influence in an obscure manner the action of some unstriped or involuntary muscles； as in the period of the peristaltic movements of the intestines； and in the contraction of the bladder。 Nor must we overlook the part which variation and natural selection may have played； for the males which succeeded in making themselves appear the most terrible to their rivals； or to their other enemies； if not of overwhelming power； will on an average have left more offspring to inherit their characteristic qualities； whatever these may be and however first acquired； than have other males。
＇20＇ ‘Lehrbuch der Histologie；' 1857； s。 82。
_The inflation of the body； and other means of exciting fear in an enemy_。Certain Amphibians and Reptiles； which either have no spines to erect； or no muscles by which they can be erected； enlarge themselves when alarmed or angry by inhaling air。 This is well known to be the case with toads and frogs。 The latter animal is made； in AEsop's fable of the ‘Ox and the Frog；' to blow itself up from vanity and envy until it burst。 This action must have been observed during the most ancient times； as； according to Mr。 Hensleigh Wedgwood；＇21＇ the word _toad_ expresses in all the languages of Europe the habit of swelling。 It has been observed with some of the exotic species in the Zoological Gardens； and Dr。 Gunther believes that it is general throughout the group。 Judging from analogy； the primary purpose probably was to make the body appear as large and frightful as possible to an enemy； but another； and perhaps more important secondary advantage is thus gained。 When frogs are seized by snakes； which are their chief enemies； they enlarge themselves wonderfully； so that if the snake be of small size； as Dr。 Gunther informs me； it cannot swallow the frog； which thus escapes being devoured。
＇21＇ ‘Dictionary of English Etymology；' p。 403。
Chameleons and some other lizards inflate themselves when angry。 Thus a species inhabiting Oregon； the _Tapaya Douglasii_； is slow in its movements and does not bite； but has a ferocious aspect； 〃when irritated it springs in a most threatening manner at anything pointed at it； at the same time opening its mouth wide and hissing audibly； after which it inflates its body； and shows other marks of anger。〃＇22＇
Several kinds of snakes likewise inflate themselves when irritated。 The puff…adder （_Clotho arietans_） is remarkable in this respect； but I believe； after carefully watching these animals； that they do not act thus for the sake of increasing their apparent bulk； but simply for inhaling a large supply of air； so as to produce their surprisingly loud； harsh； and prolonged hissing sound。 The Cobras…de…capello； when irritated； enlarge themselves a little； and hiss moderately； but； at the same time they lift their heads aloft； and dilate by means of their elongated anterior ribs； the skin on each side of the neck into a large flat disk；the so…called hood。 With their widely opened mouths； they then assume a terrific aspect。 The benefit thus derived ought to be considerable； in order to compensate for the somewhat lessened rapidity （though this is still great） with which； when dilated； they can strike at their enemies or prey； on the same principle that a broad； thin piece of wood cannot be moved through the air so quickly as a small round stick。 An innocuous snake； the _Trovidonotus macrophthalmus_； an inhabitant of India； likewise dilates its neck when irritated； and consequently is often mistaken for its compatriot； the deadly Cobra。＇23＇ This resemblance perhaps serves as some protection to the Tropidonotus。
＇21＇ See the account of the habits of this animal by Dr； Cooper； as quoted in ‘Nature；' April 27； 1871； p。 512。
＇22＇ Dr。 Gunther； ‘Reptiles of British India；' p。 262。
Another innocuous species； the Dasypeltis of South Africa； blows itself out； distends its neck； hisses and darts at an intruder。＇24＇ Many other snakes hiss under similar circumstances。 They also rapidly vibrate their protruded tongues； and this may aid in increasing their terrific appearance。
Snakes possess other means of producing sounds besides hissing。 Many years ago I observed in South America that a venomous Trigonocephalus； when disturbed； rapidly vibrated the end of its tail； which striking against the dry grass and twigs produced a rattling noise that could be distinctly heard at the distance of six feet。＇25＇ The deadly and fierce _Echis carinata_ of India produces 〃a curious prolonged； almost hissing sound in a very different manner； namely by rubbing 〃the sides of the folds of its body against each other；〃 whilst the head remains in almost the same position。 The scales on the sides； and not on other parts of the body； are strongly keeled； with the keels toothed like a saw； and as the coiled…up animal rubs its sides together； these grate against each other。＇26＇ Lastly； we have the well…known case of the Rattle…snake。 He who has merely shaken the rattle of a dead snake； can form no just idea of the sound produced by the living animal。 Professor Shaler states that it is indistinguishable from that made by the male of a large Cicada （an Homopterous insect）； which inhabits the same district。＇27＇ In the Zoological Gardens； when the rattle…snakes and puff…adders were greatly excited at the same time； I was much struck at the similarity of the sound produced by them； and although that made by the rattle…snake is louder and shriller than the hissing of the puff…adder； yet when standing at some yards distance I could scarcely distinguish the two。 For whatever purpose the sound is produced by the one species； I can hardly doubt that it serves for the same purpose in the other species； and I conclude from the threatening gestures made at the same time by many snakes； that their hissing；the rattling of the rattle…snake and of the tail of the Trigonocephalus；the grating of the scales of the Echis；and the dilatation of the hood of the Cobra； all subserve the same end； namely； to make them appear terrible to their enemies。＇28＇
＇24＇ Mr。 J。 Mansel Weale； ‘Nature；' April 27； 1871； p。 508。
＇25＇ ‘Journal of Researches during the Voyage of the 〃Beagle；〃 ' 1845； p。 96。 I have compared the rattling thus produced with that of the Rattle…snake。
＇26＇ See the account by Dr。 Anderson； Proc。 Zool。 Soc。 1871； p。 196。
＇27＇ The ‘American Naturalist；' Jan。 1872； p。 32。 I regret that I cannot follow Prof。 Shaler in believing that the rattle has been developed； by the aid of natural selection； for the sake of producing sounds which deceive and attract birds； so that they may serve as prey to the snake。
It seems at first a probable conclusion that venomous snakes； such as the foregoing； from being already so well defended by their poison…fangs； would never be attacked by any enemy； and consequently would have
｛note ＇27＇ continued｝ I do not； however； wish to doubt that the sounds may occasionally subserve this end。 But the conclusion at which I have arrived； viz。 that the rattling serves as a warning to would…be devourers； appears to me much more probable； as it connects together various classes of facts。 If this snake had acquired its rattle and the habit of rattling； for the sake of attracting prey； it does not seem probable that it would have invariably used its instrument when angered or disturbed。 Prof。 Shaler takes nearly the same view as I do of the manner of development of the rattle； and I have always held this opinion since observing the Trigonocephalus in South America。
＇28＇ From the accounts lately collected； and given in the ‘Journal of the Linnean Society；' by Airs。 Barber； on the habits of the snakes of South Africa； and from the accounts published by several writers； for instance by Lawson； of the rattle…snake in North America；it does not seem improbable that the terrific appearance of snakes and the sounds produced by them； may likewise serve in procuring prey； by paralysing； or as it is sometimes called fascinating； the smaller animals。 no need to excite additional terror。 But this is far from being the case； for they are largely preyed on in all quarters of the world by many animals。 It is well known that pigs are employed in the United States to clear districts infested with rattle…snakes； which they do most effectually。＇29＇ In England the hedgehog attacks and devours the viper。 In India； as I hear from Dr。 Jerdon； several kinds of hawks； and at least one mammal； the Herpestes； kill cobras and other venomous species；＇30＇ and so it is in South Africa。 Therefore it is by no means improbable that any sounds or signs by which the venomous species could instantly make themselves recognized as dangerous； would be of more service to them than to the innocuous species which would no