DEVELOPMENT OF THE COMMON FROG. 93 



The tadpole in the watch-glass, from which all the 

 drawings have been made, still remained in the egg-sac ; 

 but it continually" turned itself from side to side, as if the 

 confinement had become irksome. 



15. The tadpole was free and straightened to its full 

 length. A side view showed the sucker under the throat 

 in profile, a round depression in the skin near the front of 

 the head (the future nostrils), and the external gills larger 

 and more branched than before. They and the heart were 

 in active use, as the circulation in them was distinctly 

 seen, the current stopping for a moment after each beat of 

 the heart. 



The animal had grown altogether larger; and a two-inch 

 object-glass was used instead of the one-inch which had 

 hitherto been employed. 



15 (2). Two views of this tadpole were drawn, the natu- 

 ral size. 



Plate IV. 



15 (3). A tadpole with unusually large gills was selected 

 from those in the basin, and a drawing made of it. The 

 depressions for the nostrils were well marked; and it was 

 seen in this, as in the previous specimen, that the gills 

 grow out directly from the surface of each side immedi- 

 ately behind the head. 



16. A drawing of the tadpole which was examined yes- 

 terday was made, of the natural size. 



16 (2). The tadpole which has been in the watch-glass 

 from the first was examined under the microscope with 

 the two-inch object-glass. Two drawings of the under 

 surface of the head, showing the mouth and sucker, were 

 made. The upper lip was rather thick and overhanging ; 

 the lower lip was everted ; both had even edges. The sucker 

 was a large single cavity with a thick, raised rim. It 



