on the Obliquity of Flounders. 365 



nute pellucid Flounders have been described from the Medi- 

 terranean by Rafinesque (under the name of Bothus diaphanus, 

 Raf.), and by Risso (Rhombus candidissimuSy Risso). During 

 the last few years the University Museum of Copenhagen has 

 received several specimens from various parts of the Atlantic, 

 chiefly through two invaluable assistants whom Professor Steen- 

 strup has enlisted in his service in the pursuit of knowledge, 

 Captains Hygom and Andrea, to the former of whom the pre- 

 sent memoir is appropriately dedicated. The Atlantic Plagusise 

 are about an inch long, and resemble the Mediterranean forms 

 in having the eyes on the left side, and the unpaired fins pass- 

 ing on to the borders of the cheeks ; but the upper eye is rather 

 in advance of the lower, and the dorsal and abdominal unpaired 

 fins form with the tail a continuous fringe round the posterior 

 portion of the body. (PI. XVIII. fig. 2 C, C", left and right.) 

 Along with these little Flounders some other small fishes were 

 procured (fig. 2 A, A') resembling them in all particulars save in 

 this — that they were apparently quite symmetrical, with an eye 

 on each side of the head. These fishes are Flounders in an 

 earlier stage. Fig. 2 B, B' represents another form, taken along 

 with them. At B' we have the right side of the head, with an 

 eye in the normal place ; at jB we have the left side, with, strange 

 to say, two eyes in the ordinary position of the eyes of a Floun- 

 der. On careful examination, however, we find that the eye on 

 the right side is, as it were, pressed inwards into the head, that 

 a new opening surrounded by a thickened border has been pre- 

 pared for it on the left side, and that it is just on the point of 

 breaking through in the new position, being still partly visible 

 from both sides. If we hold the fish in a suitable position with 

 reference to the light, we may even trace an oblique passage up 

 through the head for the transit of the eye, through which the 

 light passes more strongly than through the surrounding parts. 

 A close examination of the stage figured 2 A shows us that it is 

 not quite so symmetrical as it appeared at first sight, but that 

 it has already undertaken many of the preliminaries towards the 

 future Flounder form. The mouth is oblique, and the eyes are 

 not seated at the same height, the left being lower than the 

 right. The sides are not equally developed ; and from the right 

 eye an oblique, more transparent path may be detected over to 

 the opposite side, up towards a point which corresponds with 

 the subsequent position of the eye. 



" More beautiful transitional steps from the symmetrical to 

 the oblique form than those represented in fig. 2 A, B, C could 

 not be given, nor more expressive evidence that the eye actually 

 goes from one side up through the head over to the other side 

 — in other words, that the symmetrical fish by degrees squints 



