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cognized as dangerous； would be of more service to them than to the innocuous species which would not be able； if attacked； to inflict any real injury。
Having said thus much about snakes； I am tempted to add a few remarks on the means by which the rattle of the rattle…snake was probably developed。 Various animals； including some lizards； either curl or vibrate their tails when excited。 This is the case with many kinds of snakes。＇31＇ In the Zoological Gardens； an innocuous species； the _Coronella Sayi_； vibrates its tail so rapidly that it becomes almost invisible。 The Trigonocephalus； before alluded to； has the same habit； and the extremity of its tail is a little enlarged； or ends in a bead。 In the Lachesis； which is so closely allied to the rattle…snake that it was placed by Linnaeus in the same genus； the tail ends in a single； large； lancet…shaped point or scale。 With some snakes the skin； as Professor Shaler remarks； 〃is more imperfectly detached from the region about the tail than at other parts of the body。〃 Now if we suppose that the end of the tail of some ancient American species was enlarged； and was covered by a single large scale； this could hardly have been cast off at the successive moults。 In this case it would have been permanently retained； and at each period of growth； as the snake grew larger； a new scale； larger than the last； would have been formed above it； and would likewise have been retained。 The foundation for the development of a rattle would thus have been laid； and it would have been habitually used； if the species； like so many others； vibrated its tail whenever it was irritated。 That the rattle has since been specially developed to serve as an efficient sound…producing instrument； there can hardly be a doubt； for even the vertebrae included within the extremity of the tail have been altered in shape and cohere。 But there is no greater improbability in various structures； such as the rattle of the rattle…snake； the lateral scales of the Echis；the neck with the included ribs of the Cobra；and the whole body of the puff…adder；having been modified for the sake of warning and frightening away their enemies； than in a bird； namely； the wonderful Secretary…hawk （_Gypogeranus_） having had its whole frame modified for the sake of killing snakes with impunity。 It is highly probable； judging from what we have before seen； that this bird would ruffle its feathers whenever it attacked a snake； and it is certain that the Herpestes； when it eagerly rushes to attack a snake； erects the hair all over its body； and especially that on its tail。＇32＇ We have also seen that some porcupines； when angered or alarmed at the sight of a snake； rapidly vibrate their tails； thus producing a peculiar sound by the striking together of the hollow quills。 So that here both the attackers and the attacked endeavour to make themselves as dreadful as possible to each other； and both possess for this purpose specialised means； which； oddly enough； are nearly the same in some of these cases。 Finally we can see that if； on the one hand； those individual snakes； which were best able to frighten away their enemies； escaped best from being devoured； and if； on the other hand； those individuals of the attacking enemy survived in larger numbers which were the best fitted for the dangerous task of killing and devouring venomous snakes； then in the one case as in the other； beneficial variations； supposing the characters in question to vary； would commonly have been preserved through the survival of the fittest。
＇29＇ See the account by Dr。 R。 Brown； in Proc。 Zool。 Soc。 1871； p。 39。 He says that as soon as a pig sees a snake it rushes upon it； and a snake makes off immediately on the appearance of a pig。
＇30＇ Dr。 Gunther remarks （‘Reptiles of British India；' p。 340） on the destruction of cobras by the ichneumon or herpestes； and whilst the cobras are young by the jungle…fowl。 It is well known that the peacock also eagerly kills snakes。
＇31＇ Prof。 Cope enumerates a number of kinds in his ‘Method of Creation of Organic Types；' read before the American Phil。 Soc。； December 15th； 1871； p。 20。 Prof。 Cope takes the same view as I do of the use of the gestures and sounds made by snakes。 I briefly alluded to this subject in the last edition of my ‘Origin of Species。' Since the passages in the text above have been printed； I have been pleased to find that Mr。 Henderson （‘The American Naturalist；' May； 1872； p。 260） also takes a similar view of the use of the rattle； namely 〃in preventing an attack from being made。〃
_The Drawing back and pressure of the Ears to the Head_。The ears through their movements are highly expressive in many animals； but in some； such as man； the higher apes； and many ruminants； they fail in this respect。 A slight difference in position serves to express in the plainest manner a different state of mind； as we may daily see in the dog； but we are here concerned only with the ears being drawn closely backwards and pressed to the head。 A savage frame of mind is thus shown； but only in the case of those animals which fight with their teeth； and the care which they take to prevent their ears being seized by their antagonists； accounts for this position。 Consequently； through habit and association； whenever they feel slightly savage； or pretend in their play to be savage； their ears are drawn back。 That this is the true explanation may be inferred from the relation which exists in very many animals between their manner of fighting and the retraction of their ears。
＇32＇ Mr。 des Voeux； in Proc。 Zool。 Soc。 1871； p。 3。
All the Carnivora fight with their canine teeth； and all； as far as I have observed； draw their ears back when feeling savage。 This may be continually seen with dogs when fighting in earnest； and with puppies fighting in play。 The movement is different from the falling down and slight drawing back of the ears； when a dog feels pleased and is caressed by his master。 The retraction of the ears may likewise be seen in kittens fighting together in their play； and in full…grown cats when really savage； as before illustrated in fig。 9 （p。 58）。 Although their ears are thus to a large extent protected； yet they often get much torn in old male cats during their mutual battles。 The same movement is very striking in tigers； leopards； &c。； whilst growling over their food in menageries。 The lynx has remarkably long ears； and their retraction； when one of these animals is approached in its cage； is very conspicuous； and is eminently expressive of its savage disposition。 Even one of the Eared Seals； the _Otariapusilla_； which has very small ears； draws them backwards； when it makes a savage rush at the legs of its keeper。
When horses fight together they use their incisors for biting； and their fore…legs for striking； much more than they do their hind…legs for kicking backwards。 This has been observed when stallions have broken loose and have fought together； and may likewise be inferred from the kind of wounds which they inflict on each other。 Every one recognizes the vicious appearance which the drawing back of the ears gives to a horse。 This movement is very different from that of listening to a sound behind。 If an ill…tempered horse in a stall is inclined to kick backwards； his ears are retracted from habit； though he has no intention or power to bite。 But when a horse throws up both hind…legs in play； as when entering an open field； or when just touched by the whip； he does not generally depress his ears； for he does not then feel vicious。 Guanacoes fight savagely with their teeth； and they must do so frequently； for I found the hides of several which I shot in Patagonia deeply scored。 So do camels； and both these animals； when savage； draw their ears closely backwards。 Guanacoes； as I have noticed； when not intending to bite； but merely to spit their offensive saliva from a distance at an intruder； retract their ears。 Even the hippopotamus； when threatening with its widely…open enormous mouth a comrade； draws back its small ears； just like a horse。
Now what a contrast is presented between the foregoing animals and cattle； sheep； or goats； which never use their teeth in fighting； and never draw back their ears when enraged！ Although sheep and goats appear such placid animals； the males often join in furious contests。 As deer form a closely related family； and as I did not know that they ever fought with their teeth； I was much surprised at the account given by Major Ross King of the Moose…deer in Canada。 He says； when 〃two males chance to meet； laying back their ears and gnashing their teeth together； they rush at each other with appalling fury。〃＇33＇ But Mr。 Bartlett informs me that some species of deer fight savagely with their teeth； so that the drawing back of the ears by the moose accords with our rule。 Several kinds of kangaroos； kept in the Zoological Gardens； fight by scratching with their fore…feet and by kicking with their hind…legs； but they never bite each other； and the keepers have never seen them draw back their ears when angered。 Rabbits fight chiefly by kicking and scratching； but they likewise bite each other； and I have known one to bite off half the tail of its antago