NOTE-BOOK OF A NATURALIST. 239 



tlie aquatic vegetables which then form its food ; and on 

 the lower lip is a small tubular process, by means of 

 which it adheres to the water-plants when taking its 

 rest. In the next stage the external gills disappear, 

 becoming covered by a membrane, and the tadpole then 

 breathes like a fish. The head, provided with eyes and 

 nostrils, has no neck, but is one with the now globular 

 trunk, largely distended by the extensive digestive canal; 

 and the large tail enables the animal to swim well and 

 strongly. In a short time the hind legs show themselves 

 near the setting on of the tail, and are soon developed. 

 Then the anterior feet are protruded ; and as the limbs 

 advance, the tail gradually lessens and shortens, shrink- 

 ing till it entirely disappears. The mouth now becomes 

 wider and loses the homy, hook-like appendages, the 

 head stands out more from the body, and the eyes are 

 furnished with lids. The belly becomes more elongated, 

 but is diminished in proportion to the size of the animal, 

 and the intestines lose much of their length. The true 

 lungs begin to be formed; and as they advance, the 

 mternal gills are gradually obliterated. Thus the whole 

 circulation is altered, and the young frog quits the water, 

 exchanging its entirely aquatic and herbivorous life for a 

 carnivorous, and, for the most part, terrestrial existence. 

 These metamorphoses, which rival those of the insects, 

 may be seen on a grander scale in the Rana ixiradoxa. 



The serpents have two auricles ; the batrachians have, 

 strictly speaking, only one, but it is separated internally 

 into two chambers. 



One word more on the discrepancies of reptile orga- 

 nization, and we will cease to pursue an inquiry, which 

 would be followed out with more aptitude in a work 

 more conversant with comparative anatomy than this 

 can pretend to be ; but the general reader, as well as the 

 student, should keep those discrepancies steadily in view. 

 The observations, however, shall be confined to the vary- 

 ing skeletons. 



