248 ZOOLOGY. 



The influence of temperature upon reptiles has already been adverted 

 to : we will only add that in the temperate zones many species exhibit a 

 winter sleep ; while this takes place in summer with inhabitants of tropical 

 regions. Soft mud, with many, forms the medium in which they spend 

 this period of repose. The probable effect upon the more vital functions 

 consists in a sluggish and interrupted circulation, and a very slight 

 respiration. Digestion must be entirely destroyed for the time. 



Witli regard to their geographical distribution, no reptiles whatever are 

 found in the far north. They occur sparingly in the higher temperate 

 regions, increasing in number to the tropics. 



The fecundity of many reptiles is very great. The frogs and toads lay 

 as many as 12,000 eggs, salamanders from 10 to 40, crocodiles from 20 to 

 GO, serpents 10 to 100, and turtles from 20 to 30. In some, as in many 

 lizards and serpents, as well as in a few salamanders, the eggs are 

 developed before exclusion from the body. This, however, must not be 

 mistaken for the viviparous placental reproduction of the mammalia. In 

 most cases the eggs are laid, covered loosely with sand, mud, or leaves, and 

 developed by the solar heat: in others, again, the animal itself incubates, 

 as in Python tigris. Special peculiarities of reproduction will be referred 

 to under the appropriate head. The external investment of the ovum may 

 be simply membranous, or else calcareous : a mucous coating is found in 

 the case of such species as deposit their eggs in the water. 



The number of reptiles is not fully known, new ones being described 

 almost every day. Upwards of 1500 are already ascertained to exist, and 

 2000 may not be beyond the maximum. The Ophidia are perhaps the 

 most numerous, and next to these the Sauria ; the Batrachia are more 

 abundant than the Chelonia. Furthermore, while serpents preponderate in 

 torrid regions, the batrachians are more properly inhabitants of the tem- 

 perate zone. Thus, in North America alone there are upwards of 80 

 species, 50 of them belonging to the urodelian, or tailed forms. 



Reptiles live partly on land alone, partly in water alone ; others, again, 

 occupy either indifferently, or at different times of the year. For this 

 reason, the latter have received the name of Amphibia from some zoolo- 

 gists. 



The flesh of reptiles is not used as food to any great extent, although 

 there is no doubt of its extreme excellence in many cases. In various 

 parts of the world, however, serpents, large saurians as the iguana and 

 alligator, turtles, frogs, &c., are favorite articles of food. The eggs of 

 turtles, and of the iguana, are highly prized. They are extracted, by some 

 South American tribes, from the oviduct of the living iguana, without any 

 serious injury to the animal. The shell of the Chelonia imbricata, or 

 hawks-bill turtle, furnishes the tortoise-shell of commerce. The teeth of 

 the alligator furnish ivory of an excellent quality. Beyond these instances 

 but little economical value attaches to reptiles. 



45!J 



