118 DR. THOMAS ALCOCK ON THE 



In the course of the first few days the single sucker 

 divides into two; and though these continue efficient almost 

 to the end of the period, they daily diminish in size, and 

 have disappeared at its close. I might perhaps have con- 

 cluded that the single sucker was an abnormal condition 

 in the individual selected, if two other tadpoles examined 

 on successive days had not shown remains of the same 

 peculiarity. 



The external gills, efficient at birth, attain their full 

 size on the second day, after which they gradually shrink, 

 but continue in action for about a week, soon after which 

 what remains of them disappears within the opercular 

 fold. The developed state of the external gills before 

 hatching was common to all the specimens under imme- 

 diate observation, which were at least a hundred in num- 

 ber; and I have noticed the same fact on other occasions. 



The clefts between the branchial arches, formed very 

 soon after hatching, have no relation to the external gills, 

 which hang freely in the water and extend, speaking com- 

 paratively, to a considerable distance from the body ; but 

 the large cilia on the surface of the lower side of the head 

 change the water in which they are bathed by the strong 

 current they produce. 



The organs which are developed during this period are 

 all completed at about the same time — that is, very nearly 

 at its close. The eyes and nostrils progress regularly from 

 the time of hatching ; but with regard to the internal gills 

 and the alimentary canal, it appears that the former are 

 commenced first, and are probably in use about the fifth 

 or sixth day in conjunction with the external gills, gra- 

 dually increasing in efficiency as the latter diminish in 

 size ; but the complete apparatus for the tadpole-respira- 

 tion is not perfected until the opercular fold has joined the 

 skin of the abdomen, leaving only a small opening at the 



