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MANUAL OF ZOOLOGY. 



respiration cutaneously, without the assistance of the lungs, 

 for a very lengthened period. This undoubted fact, however, 

 should not lead to any credence being given to the often-re- 

 peated stories of the occurrence of frogs and toads in cavities 

 in solid rock, no authenticated instance of such a phenomenon 

 being as yet known to science. 



The young or larvae of the Frogs and Toads are familiarly 

 known as " Tadpoles." The ova of the Frog are deposited in 

 masses in water, and the young form, upon exclusion from the 

 egg, presents itself as a " tailed " Amphibian, completely fish- 

 like in form, with a broad rounded head, a sac-like abdomen, 

 and a compressed swimming-tail (fig. 283, a). Behind the 



Fig. 283. Development of the common Frog (Rana temporaria). a Tadpole viewed 

 from above, showing the external branchiae (g) ', b Side view of a somewhat older 

 specimen, showing the fish-like tail ; c Older specimen, in which the hind-legs have 

 appeared ; d Specimen in which all the limbs are present, but the tail has not been 

 wholly absorbed. (After Bell.) 



mouth are placed little " holders " or organs of adhesion ; and 

 the upper and lower jaws acquire horny sheaths and con- 

 stitute a kind of beak. There are at first two sets of gills, one 

 external and the other internal. The external branchiae (fig. 

 283, a) have the form of filaments attached to the side of the 

 neck, and they disappear very shortly after birth. The inter- 

 nal branchiae are attached to cartilaginous arches, which are 

 connected with the hyoid bone, and they are contained in a 

 gill-cavity, protected by a flap of integument, which differs 

 from the gill-cover of fishes in never developing any opercular 

 bones or branchiostegal rays. Within the branchial chamber 

 thus formed the fore-limbs are budded forth, but the hind-limbs 

 are the first to appear externally, instead of the fore-limbs as 



