Page:Encyclopædia Britannica, Ninth Edition, v. 23.djvu/478

become extinct. At the time of their discovery those islands were uninhabited by man or any large mammal; the tortoises, therefore, enjoyed perfect security; and this, as well as their extraordinary degree of longevity, accounts for their enormous size and their large numbers.

Fig. 3.—Alligator Terrapin (Chelydra serpentina).

They could be captured in any quantity with the greatest ease within a few days, and proved to the ships companies who during their long voyages had to subsist mainly on salt provisions a most welcome addition to their table.

Fig. 4.—Loggerhead (Caouana caretta)

They could be carried in the hold of a ship, without food, for months, and were slaughtered as occasion required, each tortoise yielding, according to size, from 80 to 300 pounds of excellent and wholesome meat. Under these circumstances the numbers of these helpless creatures decreased so rapidly that in the beginning of this century their extermination was accomplished in the Mascarenes, and now only a few remain in a wild state in Aldabra and in some of the islands of the Gala pagos group. Singularly, the majority of these islands were in habited each by one or more peculiar forms, specifically distinct from those of the other islands.

Fig. 5.—Green Turtle (Chelonia viridls).

A large male specimen from Aldabra, which was imported into London some years ago, weighed 870 ft>, and, although known to have been more than eighty years old, was still growing at the time of its death. There is no evidence to show that any of these tortoises were indigenous in the Seychelles; the speci mens kept there in a semi-domesticated state have been either directly imported from Aldabra or are the descendants of imported individuals.

The family of Chelydridsc includes freshwater tortoises, which are known under the names of Snappers or Alli gator Terrapins (fig. 3), on account of their ferocity and long compressed crested tail. They are now confined to North America east of the Rocky Mountains, Central America, and north west South America, but remains of two species of Chelydra, closely related to their recent representative, have been found in the Oligoceue and Miocene of central Europe. A second genus, closely allied to Chelydra, Macroclcmmys temminckii, the shell of which attains to a length of 3 feet, and which is the largest known freshwater Chelonian, is restricted to the river-systems tributary to the Gulf of Mexico.

The family of Cinosternidas contains a rather large number of small-sized species, distributed from the northern parts of the United States to the northern parts of Brazil. They are of amphibious habits. The front and hind lobes of the plastron are movable, and in certain species of Cinosternum the animal can completely shut itself up in its shell.

The Chelonidae, or marine turtles, contain but few species, which are referred to three genera,—Caouana, Chelone, and Carclta. Their limbs are wholly modified into paddles, by means of which they can propel themselves with extraordinary rapidity through the water, but which are entirely unfit for locomotion on land, where the progress of these animals is as awkward as that of a seaL The toes are enclosed in a common skin, out of which only one or two claws project. The carapace is broad and much depressed, so that when the turtles are surprised on shore and turned over on their back, they cannot regain their natural position.

Fig. 6.—Hawksbill Turtle (Caretta imbricata).

Their capture forms a regular pursuit wherever they occur in any numbers. Comparatively few are caught in the open sea, others in stake nets, but the majority are intercepted at well-known periods and localities where they go ashore to deposit their eggs. These are very numerous, from 100 to 250 being produced by one female, and buried by her in the sand; they are eagerly searched for and eaten. Some of the marine turtles are highly esteemed for the delicacy of their meat and of the gelatinous skinny parts of their neck and fins; others yield oil, and others again the tortoiseshell of commerce. Probably the largest of these marine turtles is the Loggerhead (Caouana), which possesses fifteen vertebral and costal shields, and occurs in the Atlantic as well as in the Indian