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REVUE DES QUESTIONS SCIENTIFIQUES. 
L’hypothèse cle Darwin se réduit donc à ceci : 
En supposant que le serpent à sonnettes ait commencé 
par n’avoir qu’une écaille à l’extrémité de la queue, cette 
écaille n’aurait guère pu se détacher à la mue. Par suite, 
à la période suivante de croissance , une seconde écaille 
aurait dû se former au-dessus de la première, et ainsi de 
suite. Cela posé, tout l’appareil se serait développé à cause 
de son utilité comme moyen de protection contre les ennemis 
du serpent. Et en fait ces modifications ne sont pas plus dif- 
ficiles à admettre que celles, entre autres, du Secrétaire dont 
toute l’organisation a été modifiée pour lui permettre de 
chasser impunément les serpents. 
« specially developped to serve as an efficient sound-producing instrument, 
» there can hardly be a doubt; for even the vertebræ included within the 
« extremity of the tail hâve been altered in shape and cohere. But there is 
» no greater improbability in various structures, sucli as the rattle of the 
» rattle-snake, — the latéral 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 ( Gypoge- 
» ranus) having had its whole frame modified for the sake of killing snakes 
» with impunity. It is highly probable, judging from what we hâve before 
» seen, that this bird would ruffie its feathers whenever it attacked a snake ; 
» and it is certain tbat the Herpestes, when it eagerly rushes to attack a 
» snake, erects the hair ail over its body, and especially that on its tail. We 
y hâve 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 large 
» numbers which were the best fitted for the dangerous task of killing and 
y devouring venomous snakes ; — then in the one case as in the other» 
» bénéficiai variations, supposing the characters in question to vary, would 
» commonly hâve been preserved through the survival of the fittest. » 
Ch. Darwin, The expression of the émotions, p. 108-111. 
