HABITUDES. 
99 
Serpents that lead a nocturnal life are less numerous than 
those that prefer daylight to darkness. To the first cate- 
gory belong the true Dipsas, several venomous Ophidians, 
and some others ; but several serpents combine both kinds 
of life, and sometimes hunt their prey in daylight, some- 
times in the night, according to their necessities. We must 
arrange in this last class the species which have an elongated 
pupil, either vertical or transverse, which seems more parti- 
cularly adapted to contract or to dilate, according to the in- 
tensity of the luminous rays which it is necessary to receive 
into the cavity of the eye. In obscurity, the pupil thus 
formed so dilates itself, as to be entirely orbicular.^ The 
law, admitted by most naturalists, that animals with an 
elongated pupil are more especially nocturnal, is contra- 
dicted by these observations ; it seems rather that volumi- 
nous eyes indicate a nocturnal kind of life, although several 
of the genus Elaps and Naja, that have very small eyes, 
search for their prey during the night. Perhaps it is wrong 
rigorously to apply this rule to the manner of life of snakes, 
of which a good number pass a great part of their existence 
in a state of languor, or listlessness resembling sleep, and 
that do not disturb themselves, unless when some animal 
approaches them, which they seize when they are inclined, 
relapsing afterwards into a profound lethargy, which ren- 
ders them sometimes for a considerable period incapable of 
hunting for food. 
Most Ophidians choose their food indiscriminately from 
among the three first classes of vertebrate animals. The 
aquatic species, live more or less exclusively on fishes, ac- 
cording as their mode of life devotes them to the liquid ele- 
ment. The species of small size, especially the terrestrial 
and burrowing snakes, pursue insects, mollusca, worms, or 
other animals of the lower classes. Tree serpents prefer 
birds, not because this species of nutriment is better suited 
to their taste, but because it is more within their reach. 
Every body knows that serpents can, like other reptiles, 
fast for a long time. A Boa constrictor sent from Surinam 
to Holland was more than six months without the least nou- 
^ Harlan, Synopsis, p. 369. 
