Gl£NERAL ChARACTEKS.- 



-REPTILES.- 



-Gen-eral Characters. 



climates. One general inherent condition for the mul- 

 tiplication of reptiles is the reunion of equatorial heat 

 witli moisture. It is in the immense and submerged 

 savannahs or in the depths of virgin forests, in tropical 

 countries, that these creatures most abound. Hence 

 we tiiid them in such vast abundance under the ardent 

 sky uf the Moluccas, in tlie isles of Sunda and of New 

 (xuinea, where they are the terror of tlie human race. 

 Guiana too, and the intertropical parts of Africa and 



Fig, 



America, demonstrate to us the fact, that it is in tlie 

 countries near the equator tliat reptiles are most 

 numerous and most largely developed in size. 



The class Reptiles {BeptHia), according to Cuvier 

 and many other naturalists, contains the Batrachians, 

 tliat is, frogs, toads, newts, salamanders, &c., as well 

 as lizards, sei-pents, crocodiles, and tortoises. The 

 most recent s}'steniatic zoologists, however, are now 

 agreed to constitute the Batrachians into a distinct 



K-ljtliyusaurus iiitermuiiius, — Ooni^iiear' 



class, uiul.'r the name of Ainj>/iihta* or Balrachia ;\ 

 and in the following pages we shall ad<]pt this arrange- 

 ment : — 



The class Reptiles, then, thus limited, may be 

 defined — cold and red-blooded vertebrated animab, 

 with a heart trilocular, that is, formed of three cavities, 

 which consist of two auricles and one ventricle ; pos- 

 sessing true lungs, the respiration being exclusively 

 pulmonary throughout life ; having a hard and dry 

 integimient, which is generally covered with broad 

 plates or imbricated scales; oviparous, the young, that 

 is to say, being produced from eggs, which are depo- 

 sited by the mother in such situations as to be hatched 

 by the rays of the sun. 



When we say that Reptiles have cold blood, we mean 

 that their natural temperature is not much, if at all, 

 above that of the atmosphere or water iri which they 

 live ; that their power of producing animal heat is so 

 limited as scarcely to be appreciable, and therefore not 

 sufficient to prevent the system being immediately 

 affected by the loweruig of the temperature of the 

 medium by which they are surrounded. In conse- 

 quence of this, we find tliat in our climate, and in 

 countries where the temperature is low, they undergo 

 a state of torpidity in some slieltered retreat, to which 

 as a refuge instinct directs them, and where tliey remain 

 during tlie continuance of winter. The mode in whicli 

 the blood is circulated is one of the principal charac- 



• Anqihihlos {'tu.f'iii'ii)^ liaviiig a double life. 

 f Butrachos (/3»t{»x»c), a frog. 



teristics of reptiles. The heart— wdiich consists of tliree 

 cavities, viz., of two distinct auricles opening into one 

 common ventricle — transmits at each contraction only 

 a portion of tlie blood through the lungs, the rest being 

 sent directly to the other parts of the body, without 

 being specially subjected to the influence of the respira- 

 tory organs ; thus differing from the higher classes of 

 animals. Mammalia and Birds, in which the whole of 

 tlie blood must pass through the lungs before it is sent 

 back to the more distant parts of the circulating system. 

 The routine of the circulation is this : the right auricle 

 receives the vitiated blood sent from the diH'erent parts 

 of the body by the veins ; the left auricle the arterialized 

 blood returned from the lungs; and both auricles convey 

 their contents uito the caWty of the ventricle. These 

 two kinds of blood are in this ventricle mixed togetlier, 

 and part of this mixed fluid is sent through the aorta, 

 or great arterial trunk, to supply the system, and part 

 through the pulmonary arteries, to undergo a further 

 degree of oxygenation in the lungs. " It is clear then," 

 says Mr. Bell, " that the blood is by this mechanism 

 but partially changed by the action of oxygen ; in other 

 words, tliat the quantity of respiration, speaking with 

 reference to the physiological meaning of the term, is 

 comparatively small. Hence arises the circumstance 

 that these animals ha\-e what is called cold blood ; for, 

 as it is from respiration that the blood derives its heat, 

 and the temperature of the body is thereby sustained in 

 animals which have more perfect respiration, it follows 

 that where this function is but imperfectly performed, 



