THE INFANCY OF FISHES 231 



fishes, closely resembling, say, the young of cod-fish, and 

 showing no trace whatever of the strange transformation 

 which they are presently to undergo. 



There is one curious point, however, which is to be noted 

 in regard to a yet earlier stage, a point which in itself 

 seems insignificant, yet, as the sequel proves, is fraught 

 with deep meaning. Briefly, the eggs of most of the 

 right-sided species — that is to say the species in which 

 the uppermost is the right side, as in the plaice, dab, 

 flounder, lemon-dab, witch, halibut, and long-rough dab — 

 have no oil-globule ; while this is present in the left- 

 sided species like the turbot and Norwegian top-knot. 

 The eggs of the sole differ again in having a number of 

 such globules. Herein lies hid a mystery so far insoluble. 

 Very well. The larvae of flat fishes, as we have already 

 remarked, are very much like those of equal-sided fish, 

 and at first swim near the surface and feed on the minute 

 floating creatures in the same way. 



Sooner or later, however, comes the great change that 

 is to anchor them, so to speak, to the sea-floor till they 

 die. They grow deeper and deeper from back to belly, 

 and at last are unable to rest save on one side — the right 

 or left, as the case may be. The eye on the under side, 

 in any case, is in a very dangerous place, and it is clear 

 must either perish from constant contact with the ground 

 or migrate to the upper side. The latter alternative, we 

 know, has been adopted, if we may be allowed this ex- 

 pression, for it is certain that the fish can neither choose 

 nor determine the position of its eyes. What is the 

 stimulus which starts this uncanny migration of the eye, 

 and why the form of the body should compel the creature to 

 pass the whole of its adult life with one of its sides instead 

 of its back uppermost, the wisest of us cannot even guess at. 



