OEXEKAL ACCOUST OF DE^"EL0P3I£NT. 



93 



each side of the cloacal opening (Fig. 71); the limbs increase 

 steadily in size ; about the seventh week they become divided 

 into joints, and a week or so later the toga appear. T he forg _ 

 limbs anse about the same time as the hind lim bs, but are 

 covered by the opercular folds, and hence do not become visible 

 until a later stage (Figs. 84 and 85, la). 



Towards the end of the second month the Inncra come into 

 use, and the tadpoles, which now have the form shown in Fig. 

 44, 9 and 10, frequently come to the surface of the water to 



Fig. 44.- 



- Various stapes in the development of the Frog. 

 (From ISrehm's ' Thierleben.') 



1, egKS just laid, 2, eggs shortly after layiiiff. 3, tadpole shortly before liatching. 

 4, tadpoles just Ijatched. 5 and 6, tadpoles with c-xtenia' gills. 7 and 8, tadpoles with 

 ful'y formed opercular folds. 9 and 10, tadpoles with wel-developed hind legs, shortly 

 before tlie metamorphosis. 11, tadpole during the metamorphosis. 12, young frog 

 with tail only partially absorbed. 



breathe. The gills begin t o degenera te, but for some time 

 respiration is carried on both by the gills and the lungs . 



A fortmgJit or three weeks later a distinct m etamorphosis 

 occurs, whereby the t adpole becomes transformed, from the fi sh- 

 like condition in which it has hitherto been, to the purely ai r- 

 breathing stat e characteristic of the adult . The tadpole ceases 

 to f6ed ; a casting, or ecdysis, of the outer layer of the skin 

 takes place; the h omyjaw.° are thrown o ff; the l arge frille d 

 l ips shrink up ; the mo uth loses its rounded suctorial fom i and 

 becomes much wider; the tongue, previously small, increases 



