Influence of circumstances on the Actions of Animals. 1061 
viduals of its race, that the front limbs have become longer than 
the hind ones, and that its neck is much elongated; that the 
giraffe, without rising on its hind feet, elevates its head and attains 
to six metres in height (nearly twenty feet). 
Among birds, the ostriches, deprived of the faculty of flight, and 
elevated on very high limbs, truly owe their singular conformation 
to analogous circumstances. The result of habits is also as remark- 
able in carnivorous mammals as it is in the herbivorous, but it shows 
its effects in another way. In fact, those mammals who are 
habituated, as well as their race, to climb, to scratch, in order to 
excavate the earth ; to rend, to attack; to put to death other ani- 
mals which may be their prey, have had occasion to use their toes. 
Now, this habit has favored the separation of their toes, and on 
them has formed the claws with which we see them armed. 
Among the carnivores it is found that they are obliged to 
employ the chase to take their prey. Now, those of these ani- 
mals who want, and consequently have the habit of rending with 
the claws, are compelled to force them deeply into the body of the 
other animal in order to hold it, and afterwards the effort made 
to tear the seized part has, by these repeated efforts, procured for 
those nails a size and a curve which would then have impeded them 
much in walking or running on stony ground. It results in this 
case that the animal has been obliged to make efforts to draw back 
these too projecting and crooked claws, and it results in, little by ~ 
little, the formation of these peculiar grooves into which cats 
tigers, lions, etc., retract their claws when not in use. ‘Thus, 
efforts in. some directions, long-continued or habitually made by 
certain parts of a living body to satisfy wants caused by nature or 
by circumstances, increase these parts, and they acquire dimensions 
and a form which they would never have attained if these efforts 
had not become the habitual action of the animals which employ 
them. Observations made on all known animals would everywhere 
furnish examples of it. What is more striking than what the 
kangaroo offers us? This animal, which carries its little ones in the 
pouch which it has under its abdomen, has acquired the habit of 
holding itself upright, poised only on its hind feet and on its tail, 
and of moving only by the aid of a series of leaps, in which it 
preserves its upright attitude so as not to hurt its little ones, 
