OF ARTS AND SCIENCES. \) 



eye from the right side to the left takes place by means of a movement 

 of translation, accompanied and supplemented by a movement of rota- 

 tion over the frontal bone. But, in this case, very special conditions 

 attend the transfer, which, at first sight, seem to make the passage of 

 the eyes of this species an exceptional one. I think we can easily 

 show that the present mode of transfer does not differ so radically as 

 would at first seem from the conditions described in the other species, 

 in the beginning of this paper. When the right eye of the young 

 Flounder has reached the frontal bone, and approaches the base of the 

 dorsa 1 , we find, on turning the fish on his left side, that the right eye 

 is no longer on the outer surface of the right side. It no longer occu- 

 pies, as in the earliest stages, a huge orbit, capable of extensive move- 

 ments in all directions ; but unlike the left eye, which has retained all 

 its former powers of locomotion, as well as its original place, it has 

 gradually sunk deep into the tissues of the base of the dorsal fin, 

 between it and the frontal, — having sunk, indeed, to such an extent 

 that the huge orbit, so characteristic of all Flounders, has gradually 

 become reduced to a mere circular opening. Through this opening, 

 the eye now communicates with the exterior ; while, from its posi- 

 tion above the frontal (PI. X. fig. 4), it has, when the pupil turns to 

 the opposite direction, a perfectly unobstructed vision through the 

 transparent left side of the body. Little by little, the opening on the 

 right becomes smaller and smaller ; and as, at the same time, the eye 

 pushes its way deeper into the tissues, an additional opening is now 

 formed on the left side (PL X. fig. 7), through which the right eye 

 can now communicate directly with the left exterior on the left side 

 of the body. Thus, in the stage intermediate between PI. X. fig. 4 

 and PI. X. fig. 8, we find no less than three orbital openings : one 

 large one, — the original one of the left eye ; a smaller one, on the 

 left side also, the new orbit formed for the right eye, as it has 

 pushed its way through the tissues of the base of the dorsal fin ; and 

 a small orbit on the right side, the remnant of the original right 

 orbit of the right eye, which, before the right eye has completely 

 passed over to the left side, becomes entirely closed (PI. X. fig. 8). 

 With the continued sinking of the right eye, the gradual resorption 

 of the tissues, and the closing up of the old orbit, as the eye works its 

 way across the head, we eventually get the right eye entirely over to the 

 left side. It has now, by a movement of translation and of rotation, 

 penetrated through the tissues between the base of the dorsal fin 

 and the frontal bone ; having apparently passed through the head, as 

 was suggested to Steenstrup, by his examination of the alcoholic speci- 



