234 CLASS XV. 



motions also in these animals are not very different ; some are able 

 to swim and spring, others rmi and climb ; most have only a creep- 

 ing motion. A single genus alone {Draco amongst the lizards) is 

 able in some degree to fly, or ratlier flutter, by means of an expan- 

 sion of the skin along the sides of the body which is sustained by the 

 elongated ribs. One genus of a former period of the world {Ptero- 

 dactylus) was able most probably to fly in a proper sense by means 

 of a membrane which was supported by a very long finger. 



The intelligence of reptiles is very feebly developed, and in this 

 respect they stand scarcely on a higher footing than fishes. They 

 grow slowly and live long ; in temperate and cold regions they un- 

 dergo hybernation or winter-sleep ; perhaps many in warm climates 

 have a summer-sleep, whilst the rainy season causes them to emerge 

 again from their concealment. They are very tenacious of life ; 

 some remain alive for months in captivity without food ; they can 

 endure great heat and cold\ The irritability of the muscles per- 

 sists for a long time after death, as it also does in amputated parts 

 of the animal. The reproductive power is very great, especially in 

 water-salamanders ; in these not only the tail and legs that have 

 been removed grow again, but the eye also can be restored, if only 

 the entire ball as far as the optic nerve be not cut away^ 



The geographic distribution of reptiles affords occasion for some 

 general conclusions, which perhaps are the more interesting because 

 the species of this class, from being less under the influence of man 

 than those of the other classes of vertebrate animals, have not 

 been forced fi-om their original residences or introduced into other 

 regions^. In cold regions the number of genera is very small, and 

 in the tropics alone is there presented a full exhibition of this class. 



also the elaborate compilation of Ktmer Jones, in his article Heptilia in Todd's 

 CyclopcBdia, iv. pp. 273 — 287. 



^ Blumenbach observed a tree-frog, that had been stiffened and frozen in the ice, 

 come to itself again, when the ice had melted, and move and live for a long time after- 

 wards. Kleine Schriften, s. 98. 



2 Comp. C. Bonnet, (Euvres d'hist. nat. et de Philos. xi. Svo, 1781, pp. 62 — 179; 

 Blumenbach's ^ieme iScAri/'teK., s. 128 — 130. 



3 Interesting contributions to knowledge on this subject, especially in respect of 

 serpents, are to be found in H. Schlegel, Physionomie des Serpens, La Haye, 1837, 

 Svo, pp. 195—251 ; translated into English (abridged) byTnos. Stewart Trail, M.D. 

 &c. Edinburgh, 1843. 



