238 LEAVES FROM THE 



sanraSj or a plesiosaurus, i^lace it by the side of a 

 chameleon, and you will soon see, even with an unprac- 

 tised eye, how different their osseous systems are. The 

 discrepancy will be heightened if you add the skeleton 

 of a toad or a frog to the group. 



If we descend to detail, the anomaly is still greater. 

 A tortoise is toothless ; a saurian (lizard) — take a 

 crocodile, for example — is well furnished with implanted 

 teeth. Both, however, are quadrupedal, both have a 

 heart with two auricles, both lay eggs with a solid 

 calcareous shell, and the young of both are hatched in 

 the form which they retain through life, without under- 

 going any metamorphosis. A serj)ent or ophidian is 

 footless, but has a multitude of well-developed arched 

 ribs. Those which are not ovoviviparous lay eggs, with 

 a soft though calcareous covering, but their young come 

 into the world in the same shape as that borne by their 

 parents. A frog or batrachian has no ribs, or is possessed 

 of the rudiments of those bones only, and has a naked 

 skin destitute of scales. The eggs are gelatinous, and 

 laid in water. When the young are first hatched they 

 differ from theu* parents, and are furnished with branchiae 

 or gills, which, except in the perennibranchiate batra- 

 chians — Proteus, Axolotl, and Siren, for example — drop 

 off as the animal arrives at its ultimate form. The 

 metamorphosis of the anurous batrachians — those which, 

 in their perfect state, are tailless — maybe observed ever}' 

 spring by watching the development of the eggs of the 

 common frog, of which Swammerdam counted 1400 as 

 the production of one female. The greenish albumen of 

 these eggs does not coagulate easily, and the yolk or 

 vitellus is absorbed by the embryo. In the first stage of 

 its existence the tadpole, or tetard, as the French term it, 

 has a somewhat elongated body, a tail compressed at the 

 sides, and external gills. Its minute mouth is armed 

 Avith small hooks or teeth, which it plies vigorously upon 



