60 LIFE-HISTORY AND DEVELOPMENT OF 



white underneath. At the same time they push inshore, and 

 multitudes are found on muddy flats between tide-marks, and 

 in shallow rock-pools, their bodies being immersed in mud, 

 but the two active eyes raised above it. When disturbed, a 

 little streak of muddy water alone tells their course. The 

 mode by which the eye travels round has been a fruitful source 

 of discussion with scientific men, and amongst these the names 

 of Steenstrup, Malm, Schiodte, and Alex. Agassiz abroad, 



FIG. 15. Young Lemon-Dab at a later stage, the left eye just appearing 

 on the ridge of the head : enlarged. 



with Wyville Thomson and Traquair in our own country, 

 are well known. The fact is two methods exist in nature ; 

 in the one the eye travels over the ridge of the head, as 

 just described in the flounder; in the other it traverses the 

 soft and yielding tissues of the young fish, and so gains the 

 other side. In Plagusia, the species in which the latter 

 remarkable change occurs in the post-larval stage, the general 

 tissues are so transparent that the creature in a glass vessel 

 can only be noticed by the two apparently disembodied eyes, or 

 by the gleam of light caused by its movements ; and before the 

 change ensues in its eyes it can look obliquely through its own 

 body and see what passes on the other side 1 . 



Up to this stage in the life-history of both round and flat 

 fishes it will have been apparent that the efforts of man can 

 have little effect on the vast multitudes of the eggs and minute 

 fishes. His trawl sweeps beneath them, or they are carried 

 harmlessly through its meshes. Not even in a trawl blocked 

 by a fish-basket and several large skate are any likely to 



1 Alex. As;assiz, Proceed. Americ. Acad. Arts and 8c. vol. xiv. p. 8, 1878. 



