94 DR. THOMAS ALCOCK ON THE 



was wide and rounded in outline behind, but contracted 

 towards the front, until the two sides were concealed under 

 the lower lip. Within it were two plates shaped like a 

 simple leaf, with the bases attached close together in front, 

 and the points apparently free, and directed backwards. 

 The underside of the head, especially the lips and the 

 borders of the sucker, were clothed with large vibratile 

 cilia, which were in vigorous action and caused a strong 

 current from the front towards the hind part of the body. 

 The circulation was perfectly seen in the gills and in the 

 transparent parts of the body. The gills were fully de- 

 veloped ; and a slight commencement of the opercular fold 

 was seen in front of their base. 



17. A third drawing was made of the head of the tad- 

 pole, representing the mouth and sucker in profile. 



1 7 (2) . A complete drawing was made of the tadpole in 

 the watch-glass. It represented the animal with the sucker 

 in action. The form of the abdomen was a long oval. 

 The gills were not reduced in size ; but the opercular fold 

 slightly overlapped their base. The depressions of the 

 nostrils were deeper ; but there was no external appearance 

 of eyes. 



Plate V. 



18. The tadpole had grown altogether larger. The head 

 was more pointed in front and looked broader behind from 

 the growth of the opercular fold, which encroached on the 

 bases of the gills in front and formed a projecting flap on 

 each side, causing the appearance of a deep indentation 

 between the head and body when the animal was viewed 

 from above. The gills were darker in colour and less 

 transparent, from the deposition of more black pigment ; 

 and though still large, they had a slightly shrunk 

 appearance, their whole surface being corrugated. The 



