LE DARWINISME. 
93 
rapidement leur queue en produisant ainsi un son particulier 
par le frottement les uns contre les autres de leurs piquants 
creux. De sorte qu’ici les assaillants et les assaillis tout à la 
fois essaient de se rendre réciproquement aussi terribles que 
possible ; et les uns et les autres possèdent, adaptés à ce but, 
des moyens qui, par un fait assez bizarre, sont presque les 
mêmes dans certains cas. En résumé, nous pouvons com- 
prendre que si, d’une part, parmi les serpents, les individus 
mêmes qui étaient les plus propres à mettre en fuite leurs 
ennemis, ont le mieux échappé au danger d’être dévorés ; et 
si, d’autre part, parmi leurs ennemis, ceux-là ont survécu 
en plus grand nombre qui ont été le mieux doués pour la 
dangereuse tâche de tuer et de dévorer les serpents véni- 
meux; — il en résultera, dans un cas comme dans l’autre, 
que les variations utiles, en supposant variables les carac- 
tères en question, auraient été surtout conservées par la 
survivance du plus apte (1). » 
(1) <• Having said tlius much about snakes, I am tempted to add a few 
» remarks on the means by which the rattle of tke rattle-snake was probably 
» developped. Various animais, including some lizards, either curl or vibrate 
» their tails when excited. This is tlie case with many kinds of snakes. In 
» the Zoological Gardens, an innocuous species, the Coronella Sayi, 
» vibrâtes its tail so rapidly that it becomes almost invisible. The Trigono- 
» cephalus, before alluded to, bas 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 is was placed by Linnæus 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 imper - 
» fectly detached from the région 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 hâve been cast oflf at the successive moults. In this case 
» it would hâve been permanently retained, and at each period of growth, 
» as the snake grew larger, a new scale, larger than the last, would hâve 
» been formed above it, and would likewise hâve been retained. The foun- 
» dation for the development of a rattle would thus hâve been laid ; and it 
" would hâve been habitually used, if the species, like so many others, 
» vibrated its tail whenever it wa» irritated. That the rattle lias since been 
