88 



FROGS AND TOADS. 



Stage III. Disappearance of external gills. The in- 

 ternal gill stage (Fig. 19). Note the spout opening 

 on the left side. The tadpole is now fish-like in many 

 important structural and functional characters. 



Fig. 20. Tadpole with hind limbs. 

 It shows also the " spout" open- 

 ing on the left side. 



Fig. 21. Tadpole showing fore 

 limbs beneath the skin. 



Stage IV. Appearance of hind limbs (Fig. 20) . 



Stage V. Appearance of fore limbs. Note that the spout 

 opening is quite visible until the fore limbs begin to 

 bulge. With a good lens the fore limbs with out- 

 spread toes may be seen under the skin (Fig. 21). 



Stage VI. Tail entirely gone. Frog stage is reache^ 



