Redi, in the beginning of November, made a large opening in the skull of a Land-Tortoise, extracted the brain, and cleaned out the cavity. He then set the animal at liberty, and it groped its way freely about wherever it pleased, as if it had not been injured. Redi makes use of the term 'groping' (brancolando), because he says that when the tortoise was deprived of its brain it closed its eyes, which it never again opened. The wound which was left open skinned over in three days, and the tortoise, continuing to go about and execute other movements, lived to the middle of May. On a post-mortem examination the cavity which the brain had occupied was found empty and clean, with the exception of a small dry and black clot of blood. He repeated this experiment upon many other Land-Tortoises in the months of November, January, February, and March, with this differ ence, that some were locomotive at their pleasure, whilst others, though they made other motions, did not move about : he found the same results when he treated Fresh-Water Tortoises in the same manner, but they did not live so long as the terrestrial species. Ha states his belief that the Marine Tortoises would live a long time without their brain, for he received a turtle which he treated in the same way, and though it was much spent and faint from having been long out of the sea, it lived six days. In November he deprived a large tortoise of its head, without which it continued to live twenty three days : it did not move about as those did whose brain had been taken out, but when its fora or hind legs were pricked or poked, it drew them up with great strength, and executed many other move ments. To assure himself beyond all doubt that life, such as it was, continued in such cases, he cut off the heads of four other tortoises, and on opening two, twelve days afterwards, he saw the heart beat and the blood enter and leave it We have already had occasion to call attention to the great length of time during which these reptiles will live without food, and the facts above recorded afford additional proof of their extreme tenacity of life.
Touch.—In the greater part of this order, skin, properly so called, does not exist at all on certain parts of the body, or is reduced to a delicate fibrous plate applied like a simple periostaum on the bones of the head and on the external parts of the vertebrm of the back, the ribs, and sternum. The Soft Tortoises (Trionyx and .5phargis, for instance) are the only ones that differ in this respect. Nevertheless the neck, the feet, and most frequently a considerable part of the tail, are covered with a true flexible skin. This skin in the Matamata is fringed, or furnished with moveable appendages on the lateral parts of the head and neck. There can be no doubt that the sort of touch or sensation which will indicate to a Trionyx, or even to a Marine or Land-Tortoise, the differences of temperature that affect the medium wherein it moves, is preaeut in those animals, but the sensibility of a true touch must be very much blunted in them. Some have their toes united down to the nails, or father hoofs, and absolutely immoveable ; others have them flattened, and forming a sort of paddle, as in Chelone and Sphargie ; or the whole foot terminates by a sort of shapeless stump, rounded like that of the elephant, the presence of the toes being only indicated by those nails or hoofs, as in the Land-Tortoises.
Others, it is true, Emys, Trionyx, and Chelys, for example, have their toes very distinct, but they are nevertheless united by membranes, and In general their feet seem more adapted for the different modes of transport than for touch. The Matamata indeed has its nose prolonged into a sort of moveable proboscis; but this organisation seems to be directed more to favour the required mode of respiration, than to give the animal that sort of perception exercised by the snout of swine and the muzzles of moles and some shrews. (Dumeril and Bibron.) Taste.—The wide fleshy tongue, with its distinct papillae, like those of Mammals, seems well calculated for tasting vegetable and animal juices after the food is minced up by the horny mandibles; the fleshy lips on the outside of these mandibles in the Trionyces probably assist in retaining these juices.
SmelL—Though there is probably sufficient of this sense to assist the animal in its discrimination of food, and aid the functions of the tongue in giving the animal a perception of flavour, it may be con cluded from the very simple state of the organs, so different from the complication of those in animals where the eensa is known to be highly developed, that it is not very acute in the tortoises.
Hearing.—From the structure of the internal ear, to which we have before alluded, it might be inferred that this function is tolerably acute, but many of the species appear very insensible to sound.
Sight —The eye is well developed and is large. It is modified ao as to be adapted to the medium, whether air or water, through which the light is to be transmitted. In the substance of the cornea scales or osseous plates are found analogous to those in birds, and there are three eyelids and two lachrymal glands.
Reproduction.—According to tho accounts of voyagers the Coriaceous Tortoises (Sphargis) and the Trionyces seem to pair, and two indivi duals of different sexes remain constantly together in the same places. The great Marine Tortoises, as is well known, come every year at their appointed times to deposit their eggs in the sand on the shores of the sea and banks of rivers near strands of gentle declivity. There the females hollow out a sort of rude but strong vaulted nest or oven, as it may be termed, wherein the eggs may have the benefit of the con centrated rays of the sun, so as to enjoy an equable heat, as in the case of eggs under a sitting hen, but under circumstances which do not permit the body of the mother to impart the necessary warmth. The shell of these eggs is generally solid, and their form globular, or of a short cylindrical shape equally rounded at the extremities. A female Turtle will lay as many as a hundred at one time. The plastron of the males of many species of Chelonia is concave, that of the females being convex. Messrs. Dumeril and Bibron say that in the Qheloniana and Anourous Batrachians from eighteen to thirty-one days and more have elapsed before the male has quitted the female.