90 OUR REPTILES. 



fallen off, they have not been cast off by a species of moult- 

 ing, as in the case of insect larvae. They have been got rid 

 of by none of these methods ; their substance has been re- 

 absorbed, atom by atom ; and hence, although it has ceased 

 to exist, it is not the less alive on that account. 



We see, then, that frogs undergo complete metamorphoses 

 not only in regard to their entire organism, but as to each 

 set of apparatus, with the exception of the nervous system. 

 The salamanders are not similarly situated. These maintain 

 their external gills throughout the entire larval period, and 

 never acquire internal branchiae. When reaching the air- 

 breathing condition, they skip, as it were, one of the trans- 

 formations which frogs undergo. The salamanders have 

 also four legs in the perfect state ; but then, in addition to 

 these, they preserve the tail* 



Frogs spawn most commonly about the middle 

 of March. A large number of small round 

 opaque bodies, enclosed in a glairy mass, are 

 deposited at the bottom of pools and ditches. 

 Speedily, by the absorption of water, the enve- 

 lope swells, and each ovum, like a little black 

 dot, is enclosed within its sphere of gelatine. 

 These masses of ova soon rise and float on the 

 surface of the water, in which state they are 

 known to all country people as " frog spawn/' 



At first the embryo is a small globular body, 

 rather darker on one side than the other. In 

 about four-and-twenty hours the sphere elon- 

 gates, and in eight-and-forty hours the presence 



* " Metamorphoses of Man and the Lower Animals." 

 Translated by Dr. Lawson. London : Hardwicke. 



