28 ATLAS OF BIOLOGY. 



FIG. X ft . The same, from the left side. 

 FIG. X h . The anterior end of the above, ventral view. 



FIG. XI. The tadpole, at the first appearance of external gills, body segments and the 

 organs of the higher senses. 



The animal is at this period still enclosed within the egg-membranes, the tail being 

 curved to one side as indicated. 



FIG. XP. The head of the same, ventral view. 



FIG. XII. The tadpole, on the assumption of the free swimming stage. The external 

 gills are at their maximum. Dorsal view. 



FIG. XTI a . The head of the same seen from beneath. 

 FIG. XII 1 '. The root of the tail of the same, ventral view. 



FIG. XIII. The head of a tadpole, on the appearance of the opercular fold, seen from 

 the left side. 



FIG. XIV. The tadpole's head, during the period at which external and internal gills 

 coexist. Ventral view. 



FIG. XIV a . The same, the branchial chamber being opened up on the right side. 



FIG. XV. The tadpole, at the period in which the last remnants of suckers and first 

 traces of hind limbs are visible. Ventral view. 



FIG. XV a . The same. 



Both branchial chamber and body-cavity having been opened up, showing that internal 

 gills and lungs coexist. 



FIG. XVI. A late stage of the frog's tadpole. 



Both fore and hind limbs are visible, the former still buried up beneath the larval 

 integument. Ventral view. 



FIG. XVII- The late larva, on the assumption of a prehensile-mouthed exclusively 

 air-breathing stage. The tail was partly absorbed. Seen from the left side. 



(Figs. X. to XVII. all x 5.) 



FIG. XVIII. Longitudinal vertical section of the embryo, at a stage slightly earlier 

 than that of Fig. X. x 10. 



FIG. XIX. A similar section of a later tadpole.* 

 From nature, after Goette (8). x 10. 



* The blastopore is stated bj- Spencer (Zwil, ^n^,, February 23rd, 1885) to persist as the apus. 



