382 On the Position of the Eyes in Pleuronectidje. 



14 millims., and 40 millims. long, that tlie development of the 

 position of the eyes after hatching is upon the whole a very 

 slow process, and that consequently the position of the eye on 

 the future blind side can scarcely have been quite symmetrical 

 even in the new-born fish. In the young fish of 10 millims. 

 length the anomalous eye has abeady, in every essential par- 

 ticular, the same position with regard to the bones of the skull 

 as in the adult, being placed in its orbit ; and I therefore con- 

 sider it in the highest degree probable that the arrangement 

 of the frontal and anterior frontal bones round the eye of the 

 future blind side takes place in all essential points already in 

 the embryonal state ; nor could the matter very well be ima- 

 gined othei-wise according to all we know about the formation 

 of the embryo. But then the whole case falls under a very 

 well-known biological law, and becomes plain enough. The 

 young PleuronectidcB are born with a position of their eyes 

 calculated for life nearer the surface of the water, and grow 

 slowly and gradually more asymmetrical in proportion as the 

 adult fishes seek more the bottom of the sea, or, at any rate, 

 are more calculated upon movement along a firmer surface *. 

 Hence the well-known long series of forms exhibiting a gra- 

 dual transition, from Hipijoglossus pinguis^ which does not in 

 any considerable degree alter the shape in which it leaves the 

 ovum, to the soles, which are entirely thrown on one side. It 

 appears, however, that Hippoglossus pinguis is not the least 

 asymmetrical form of the family. I have before me two perhaps 

 not quite adult specimens of an apparently undescribed oceanic 

 flounder, taken in the Atlantic, which I propose to call Bas- 

 canius tcedifer^ n. s., and which, in the series above alluded 

 to, would take place before the Ilippoglossus. It is, as is the 

 case with other oceanic animals, clear as water, very high and 

 narrow, about 25 millims. long, foliaceous, almost symme- 

 trical ; only the left side is a little more developed, and the 

 eye on that side is placed a little lower on the head. The 

 greatest height of the body is at the commencement of the 

 anal fin, where it almost reaches one-half of the total length. 

 The muciparous canal makes a very slight bend over the 

 pectoral fin. The dorsal fin reaches the nostrils in front, and 

 approaches behind (as also does the anal fin) close to the caudal 

 fin, which is slightly roimded at the end ; the open space be- 

 tween the ventral fin and the anal fin is longer than the 

 ventral fin itself. The rays of the fins exhibit only few 

 and long joints ; their number I find to be in my two spe- 



* Monstrosities, caused by the eye of the blind side being an-ested in 

 its process of transfer in front of the dorsal fin, have long been known. 

 Comp. Dr. Traquair's treatise, p, 265. 



