BATKACHIAN AMPHIBIA. 371 



ing a sort of membranous operculum. A little later the 

 branchiae become ramified, and the lips are covered with 

 a minute horny beak, by the aid of which the little animal 

 fixes itself to vegetables that form its chief food ; but this 

 state does not last long. At the end of a few days the 

 branchial fringes, appended to each side of the neck, 

 begin to disappear (Fig. 3016), and respiration is carried 

 on by means of small tufts of blood-vessels, placed along 

 four cartilaginous arches, situated under the throat. A 

 membranous tunic, covered by the skin, envelopes these 

 internal branchiae, to which the water arrives by the 

 mouth, and, after having laved these organs, escapes 

 through one or two external slits, the situation of which 

 varies a little in different species. The respiratory appa- 

 ratus, now, exactly resembles that of fishes. Some time 

 afterwards the hinder legs of the tadpole show themselves, 

 and are developed little by little (Fig. 30 Ic). These attain 

 considerable length before the front legs are perceived 

 baneath the skin, which at a later period they penetrate. 

 About the same time the horny beak falls off, leaving 

 the jaws unencumbered. The tail begins to waste away ; 

 the lungs are developed, and, in proportion as these organs 

 become more exclusively the seat of respiration, the 

 branchiae fade and disappear. Finally, in Frogs and 

 Toads the tail is altogether lost, the animal assumes 

 the form that it preserves through life, and completely 

 changes its regimen. From being at first herbivorous, it 

 gradually becomes exclusively carnivorous, and all its 

 digestive apparatus is changed accordingly. The period 

 of these changes varies from about four to eight weeks, 

 according to the species; and it has been ascertained that 

 different circumstances may considerably hasten or retard 

 the completion of their metamorphosis. A deficiency 

 of light and heat very much prolongs the duration of the 

 tadpole state. 



Having reached their perfect condition, the frogs cease 

 to be aquatic animals ; but most of them continue to live 

 in the neighbourhood of water, and dive frequently into it. 



The Batrachia are divisible into two sections, those 

 t^iat preserve their tail in their adult state (Urodela), 

 and those that lose that member altogether (Anoura). 

 Those that retain their tail walk badly : owing to the 

 feebleness of their limbs they can only drag their 



