REPTILES. 



845 



In the Linnaean Transactions and Zoological 

 Journal are some interesting papers on Reptiles 

 by Mr Thomas Bell. His monography of the tor- 

 toises having a moveable sternum in the 2d volume 

 of the Zoological Journal, and also his essay on 

 Lcptophina, a group of serpents, contain some 

 valuable additions to our knowledge of reptiles. 



The heart in reptiles is so constructed, that at 

 each of its contractions, only a portion of the blood 

 which it receives is transmitted to the lungs, the 

 remainder of this fluid is returned to circulate 

 again, without having passed into the lungs, and, 

 consequently without having been subjected to 

 respiration ; hence it results that the action of 

 oxygen on the blood is greatly less than in inamini- 

 ferous animals and birds, where all the blood, by 

 passing through their lungs, is exposed to the 

 action of the air. Consequently, as respiration 

 causes the heat in the blood, and gives to the mus- 

 cular fibre its susceptibility for nervous irritation, 

 the temperature of reptiles is much lower, and their 

 muscular power greatly weaker than that of the 

 mammalia, and birds. Therefore they are said to 

 be cold-blooded animals. Their general habits are 

 also much less energetic, almost all their motions 

 consisting of crawling and swimming, and although 

 several species run or leap, at times with consider- 

 able facility, yet upon the whole, their actions are 

 sluggish, and their sensations obtuse, with a slow 

 digestion ; and in temperate countries they pass 

 the winter in an almost constant state of torpidity. 



The brain in reptiles is proportionably small, and 

 not so essential to the exercise of their animal and 

 vital functions as to the mammalia and birds ; and 

 their sensations appear to be referred to a common 

 centre, for they continue to live, and exhibit vol- 

 untary motions long after being deprived of their 

 brain, and in many instances after the head has 

 been cut off. The connection of the nervous sys- 

 tem with the muscular fibre is also less necessary 

 to its contractions, and their muscles preserve their 

 iiritability after being severed from the body much 

 longer than in the higher animals. The pulsations 

 of the heart have been known to continue for many 

 hours after being separated from the body; and even 

 without it, the body will move for a considerable 

 length of time. It has been observed that the 

 cerebellum in several of the species is extremely 

 small, which fact agrees with their slight propensity 

 to motion. 



The smallness of the pulmonary vessels in rep- 

 tiles enables them to suspend respiration without 

 retarding the circulation of the blood ; this enables 

 them to dive with more facility, and to remain 

 longer under water than quadrupeds or birds. The 

 cells of their lungs are also less numerous, and 

 generally large, in consequence of their having 

 fewer vessels to lodge on their parietes, and the 

 lungs take sometimes the form of simple sacs, 

 scarcely cellular in their structure. 



The whole class are provided with a trachea and 

 larynx, yet many of them are incapable of producing 

 articulate sounds. 



As their blood is cold, teguments for retaining 

 heat are unnecessary, and instead of these, there- 

 fore, they are clothed with scales, or simply with a 

 naked skin. 



The females are provided with a double ovary 

 and two oviducts, and the males of several genera 

 are furnished with furcated organs of generation, 

 but the batrachians are destitute of this organ. 

 Those females which couple deposit eggs which 

 are protected by a shelly covering, and those spe- 

 cies which do not, produce soft and glary eggs, 

 destitute of any crust. These they abandon after 



the deposition in some convenient situation ; but 

 there are a few species which carry them about 

 with them. The young is hatched perfect in ita 

 form in many species : but there are other species, 

 which, on quitting the ova, have the organization 

 of fishes, and whose form is not perfectly developed 

 until after a certain time has elapsed, when they 

 undergo a complete metamorphosis. This is well 

 exemplified in the frog being hatched as a tadpole. 

 These are provided with branchiaB, or gills, like 

 fishes, and some of the genera retain these organs 

 even after the development of their lungs. In sev- 

 eral of the oviparous reptiles, particularly in the 

 coluber, the young animal in the egg is formed and 

 considerably advanced at the moment it is deposited 

 by the mother ; and there are even some species 

 which may be artificially rendered viviparous, by 

 simply retarding the time of laying the egg, which 

 M. Geoffrey St Hilaire has proved by depriving the 

 colubra of water. 



The quantity of respiration in reptiles is not 

 fixed, as is the case with mammalia and birds, but 

 varies with the proportions of the diameter of the 

 pulmonary artery, compared to that of the aorta. 

 Tortoises and lizards, for example, respire much 

 more than frogs, &c.; and hence results a much 

 greater difference of sensibility and nervous energy 

 than can exist between one mammiferous animal 

 and another, or between birds. 



A greater variety of form prevails amongst rep- 

 tiles than is found among the mammalia and birds, 

 and it is in the production of these forms that Na- 

 ture seems to have imagined shapes of the most 

 fantastic description, and modifying in every pos- 

 sible manner the general plan which she has pre- 

 scribed to herself in the vertebrata, and in the ovi- 

 parous class in particular. 



Reptiles are endowed with five senses, but none 

 of them in great perfection. In those species which 

 are covered with scales or plates, the sense of 

 touch is very obtuse ; and in the species which 

 have a naked skin, such as the frog, it is also weak, 

 in consequence of not being adherent to the body, 

 but envelopes it like a bag. In the serpents, the 

 eyes are immoveable, and are destitute of eyelids ; 

 and the eyes covered with a corneous substance ; 

 in some genera, three eyelids are distinguishable, 

 while others are destitute of sight. They have no 

 cochlea, and only provided with a small bone under 

 the tympanum. Their nostrils are small, and they 

 appear to have a very weak sense of smell. They 

 have no delicacy of taste, for almost all the species 

 swallow their food entire, and those in which the 

 tongue is soft and flexible, this organ serves chiefly 

 as an instrument for the seizure of their food. None 

 of them have true fleshy lips ; and some, such as 

 the tortoises, are provided with a horny bill, like 

 that of a parrot ; others have teeth of various 

 forms, which are not, however, formed for mastica- 

 tion, but to assist in holding their prey : various 

 serpents have hollow fangs, which they can erect 

 at pleasure, when they open their mouths to bite, 

 and these fangs have apertures, from which they 

 inject into the wounds made by them an active and 

 deadly poison. The anal opening in serpents 

 serves for rejected matters, as well as for organs of 

 generation. 



The physical construction of reptiles varies con- 

 siderably in the different orders ; deviating in 

 several essential particulars, to which no general 

 characters will apply. The following is an outline 

 of these particulars. 



I. The Cm I.CI.MA, or Tortoisos, have a heart with two au- 

 ricles, and a ventricle, divided into two unequal cavities, 

 which communicate with ear h other. The blood from the 

 body is poured into the right auricle, wul from the luiigsiutu 



