12 



C H E L O N I A. 



drinking than to ordinary breathing-. The whole is 

 performed by the action of the mouth, at least in all 

 the species which have the scaly plates irnmoveable. 

 The os hyoides, or bone of the tongue, is the principal 

 organ of support in the performance of this somewhat 

 curious process. When these creatures breathe, 

 they do not open the mouth, as is the case with most 

 of those animals which require a more frequent and 

 copious supply of air. On the other hand, they keep 

 the jaws firmly closed (and there are no animals 

 which can close them more firmly), and perform the 

 respiration by means of the action chiefly of the 

 tongue. By depressing the os hyoides, they open the 

 nostrils, and at the same time form an open cavity of 

 considerable extent in the mouth, into which the air 

 rushes. Then, when the cavity thus formed is filled 

 with air, the os hyoides is raised, which closes the 

 apertures of the nostrils, and at the same time, by 

 lessening the cavity of the mouth, forces the air into 

 the lungs, which of themselves perform the operation 

 of expelling the air after it has performed its function. 



It will be seen that this species of breathing has 

 much more of a voluntary process than that of the 

 higher animals, which require the operation much 

 more frequently, and that thus it can be suspended at 

 the pleasure of the animal. The same kind of respi- 

 ration takes place in the Batrachia, and indeed to a 

 greater or less extent in the whole class of reptiles. 

 See REPTILES. 



In the armature of their jaws the chelonia have 

 some resemblance to birds, and indeed there are 

 many more structural coincidences between the two 

 than we would be prepared to expect in animals 

 which are so different both in their appearance ami J 

 their habits. Generally speaking, the jaws of the j 

 chelonia are covered with horny plates, not very I 

 unlike the mandibles of birds ; but in the texture of 

 this horny substance there appears to be a general 

 law in the species those which have the bucklers of 

 the firmest texture have the coverings of the jaws 

 firmest ; while the soft tortoises, which have only a 

 thick parchment-like skin for their covering, have the 

 jaws covered with a similar skin. When we say 

 "shell," in the case of these animals, we must not be 

 understood to mean shell properly so called, that is, 

 shell containing salts of lime, which can retain their 

 form after all the animal matter has been destroyed 

 by burning ; for even the most compact of their 

 coverings, the shell of the hawk's-bill turtle, the true 

 tortoise-shell, of which so many trinkets, and other 

 little ornamental matters, are made, approaches much 

 more nearly in substance to horn than to any thing 

 else with which we can compare it. The chief differ- 

 ence, indeed, is in the texture, which is not fibrous, 

 but rather composed of small laminae, which admit of 

 division with almost equal readiness in all directions. 

 The substance to which it approaches most nearly is 

 that of hoofs, more especially the hoofs of antelopes. 

 But it is really horn, and can be softened and treated 

 exactly in the same manner as other horny sub- 

 stances. There is a gradation in the production of 

 horny substance, which is worthy of more careful 

 examination and study than it has hitherto met with. 

 The loosest texture with which we are acquainted is 

 that of baleen, on the plates of whalebone in the 

 large Greenland whale. This substance is little else 

 than soldered hairs, and hairs not very closely or 

 firmly soldered, as they can be very easily separated 

 from Ciich other, though even these arc more cusilv 



separated into plates than into fibres. From them 

 there is a gradation ; and it is not a little singular 

 that we meet with the other extreme of the series in 

 an aquatic animal, the hawk's-bi!! turtle, and also that 

 the firmness of texture in thin substance appears to be 

 in proportion to the sluggishness of living action in 

 the animals in which it is found. It is also worthy 

 of remark, that the animals in which this substance 

 is found are tenacious of life, very much in the ratio 

 of the firmness of the substance. 



Perhaps when we consider the matter physiologi- 

 cally, we ought to be prepared for expecting this. 

 The principle of life in animals, of what class soever 

 they may be, is a principle at variance with or opposed 

 to the principle by which substances are brought into 

 contact, and retained there to all the attractions of 

 gravitation and aggregation, in short ; and we find 

 that, in all animals, indeed in all organised beings, the 

 departure from the common homogeneous structure, 

 which matter, in obedience to those laws which have 

 no principle of life in them, invariably assumes, is 

 always in proportion to the energy of living action in 

 the animal or the vegetable. The lowest, that is the 

 least energetic in life, of vegetables and of animals are 

 the most uniform and jelly-like in their structures ; and 

 the farther that we ascend in the scale of being, we find 

 that there is always the more organisation. We find 

 also that, in proportion as the organic being departs 

 more from the ordinary laws of inorganic matter, it 

 costs it the more labour to maintain the life. The 

 higher animal must breathe frequently ; and its blood 

 cannot pass a second time into the circulation, or be 

 able to perform its functions in the body, without 

 being fully and freely exposed to the action of the 

 renovating atmosphere ; while, in those creatures in 

 which life is less energetic, the action of a limited 

 portion of the blood suffices, and even that may be 

 suspended for a considerable time at the will of the 

 animal, and is all but entirely suspended when they 

 are in a state of hybernation. Even when they are 

 not in a state of absolute hybernation, these animals 

 can be kept alive for a considerable time without 

 respiration. Some of them have lived for at least a 

 month with the jaws firmly tied together, and the 

 nose sealed up with wax, in which state they of course 

 could neither eat nor breathe. As they have not 

 much free action of air in the mouth, they have little 

 voice, and the little which they do have is a sort of 

 murmuring hiss produced by the violent compression 

 of the lungs by those abdominal muscles which they 

 use in expelling the air from these organs. 



In the mode of bringing forward their eggs to the 

 period when they are fit for deposition, these ani- 

 mals have some resemblance to birds ; but the albu- 

 minous or white part of the egg does not coagulate 

 with heat. The covering of their eggs also differs 

 considerably from that of the eggs of birds, the hardest 

 having more resemblance to indurated parchment or 

 vellum than to common egg-shell. 



Though some of them are inhabitants of temperate 

 climates, and many take up their abodes chiefly in 

 the waters, or in rnuddy places where the temperature 

 is always low, yet they are all unable to bear extremes 

 either of heat or of cold ; and there are certainly few 

 species which do not, during some part of the year, 

 seek the mean temperature by digging into the earth, 

 or burrowing in the banks. It is even probable that 

 some of the marine species plunge to a considerable 

 depth at some seasons of the year, and remain there, 



