The eyes have, besides the lower and upper lid, a third, the nictitating membrane, which can be drawn over the front of the eyeball. In the upper lid lies a cup-shaped bony plate of variable size. The pupil contracts into a vertical slit. The iris is greenish.
Fig. 104.–Map to illustrate the present distribution of Crocodilia.
The recent geographical distribution of the various kinds of Crocodilia loses its mystery when we recollect that during the Tertiary period Alligators, Crocodiles, and long-snouted Gavials existed in Europe. The solitary species of Alligator in China is the last living reminder of their former Periarctic distribution. The group, taken as a whole, is otherwise now intertropical, Crocodiles alone inhabiting the Palaeo-tropical region, together with long-snouted forms in the Oriental sub-region, while Alligators and Caimans, with a few Crocodiles, live in America.
They are all rapacious, doing much damage by their predatory habits, and are fierce and sulky in temper. But the danger to man differs much in different countries. While Crocodiles are dreaded in some localities, they are in others considered almost harmless, and men swim through the haunted waters without hesitation. It seems as if certain old and wily individuals turn into man-eaters, just like tigers and lions.
Their home is the water, in which they pass the night, their time of hunting. The prey is either patiently watched or stalked, and nothing falls amiss. Water-birds are seized by the beast, which rises imperceptibly from below. Some species are said to make use of their powerful tails for hitting the victim and even jerking it into the mouth. The strength of their jaws is enormous, and they do not let go what they have seized, unless, in the case of a man, he has the presence of mind and the opportunity to dig his fingers into the monster's eyes whilst being dragged down.
In the morning they crawl on to sandbanks, or on to logs of wood, which they closely resemble, in order to bask, mostly in such a position that on the slightest alarm they can plunge into the water. For this reason they frequently make a half circle before they settle down to rest, with the heads turned towards the river. There they bask all day long, apparently fast asleep, often with gaping mouths. But their sense of hearing and of sight is sharp, and they learn from experience, old individuals being by far the most wary. Commercially the skins are now of considerable value. The flesh is white, and is tolerable eating but for the combination of fishy and musky odour, which, although faint, is not to everybody's liking.
All the species have a voice, a kind of loud, short bark or croak, heard at night and when angered. The female lays several dozen or even three score white, oval, hard-shelled eggs in the sand, well out of the reach of moisture; and some species construct an elaborate kind of nest. The mother watches it, takes care of and fights for her offspring, numbers of which fall an easy prey to large storks, fishes, and to the stronger members of their own kind.
In the cooler countries they hibernate in the ground; and in hot countries, which are subject to drought, some kinds aestivate in the hardened mud; or they migrate. When during a prolonged drought on the island of Marajó, at the mouth of the Amazon, the swamps and lakes were dried up, the Alligators migrated towards the nearest rivers, and many perished in the attempt. On one farm were found 8500 dead, and at the end of Lake Arary more than 4000. Such occurrences in bygone times may perhaps explain the masses of bones found here and there in a fossil state.
The age to which Crocodiles can live is quite beyond calculation. They are capable of propagation long before they are anything like half-grown, maybe at an age of little more than ten years; then they continue to grow perhaps for more than one hundred years, until they die.