The Zoologist— March, 1869. 1673 



portion remaining being usually on the upper part of the tail. The 

 absorption extended below the dorsal surface, leaving at first a 

 groove along the back, marking the position of the membrane ; 

 and as this disappeared the light-coloured specimens retained in 

 its place a narrow black line, which extended also to the end of 

 the tail. 



The absorption of the external branchiae was the next marked 

 feature in the transformation, although this also commenced before 

 the changes just mentioned were completed. The atrophy apparently 

 began at the extremities of the branchial processes, and when these 

 had diminished to about half their natural size, and the fimbrijE had 

 disappeared, the ends rolled up underneath, leaving the remnants as 

 rounded tubercles, which, in some of the specimens remained long 

 after all the other stages of the transformation were passed. The 

 absorption, moreover, did not always proceed with equal rapidity on 

 the two sides of the same animal, but in one instance stumps of the 

 processes were retained on one side some time after those on the other 

 had disappeared. During the diminution of the external branchiae, 

 the internal vascular arches which support the external processes also 

 became absorbed. As these disappeared the orifices on either side of 

 the neck and the open fold of the throat became closed by the adhesion 

 of the opercular flap to the surface below, leaving, especially in the 

 gular region, a deep cicatrix. These changes, which were in each 

 case apparently completed before the remnants of the external 

 branchiae had disappeared, were evidently the main cause of a 

 marked alteration in the shape of the head, which occurred about 

 the same time. In the siredon state the head is broadest at the base, 

 and comparatively flat above, but after the loss of the branchial 

 arches its greatest breadth was a little behind the eyes, while it was 

 much more rounded above, and in outline more oval. The neck also 

 diminished in size, and the snout became more pointed. The change 

 in the eyes, already alluded to, likewise altered the appearance of the 

 head materially. The flat, fish-like eye of the siredon projected very 

 slightly above the surface of the head, but during the transformation 

 this organ became more convex, and also much more prominent. 

 This change in the eye was apparently indicated also in the habits of 

 the animal. The siredons seldom missed their aim in catching a 

 worm or insect, but when under water after the metamorphosis 

 they often made several ineflfeclual attempts to seize objects quite 

 near them. 



