DEVELOPMENT. 



299 



glossidae the openings converge and combine into one median 

 ventral opening. In other Aiiura the right opening passes on 

 to the left side and combines with the left, so that there is only- 

 one spiracle, as these openings are called, on the left side of the 

 body. 



The intestine of tlie tadpole is long and spirally coiled. At 

 the metamorphosis the animal undergoes an ecdysis, with which 

 is connected the appearance of the anterior limbs, the closure 



Fig. 171. — Later stages in the development of Pelobates fuseus. a, larva without limbs, with 

 well -developed tail, b, older larva with hind limbs, c, larva with two pairs of limbs. 

 d, young frog with caudal stump, e, young frog after complete atrophy of tail. 



of the gill-slits and the absorption of the internal gills. The 

 horny beak is cast off, and the eyes which have hitherto been 

 concealed beneath the skin appear on the surface and are of 

 considerable size. The larva has now become an exclusively 

 ail'- breathing four-legged adult, which has only to lose its 

 swimming tail in order to acquire its definitive form (Fig. 171). 

 The duration of tadpole life is usually considerable (some 

 months) and during the later stages the larva breathes by its 



