OF ARTS AND SCIENCES. 5 



in Pis. III. and IV. ; with the exception, of course, that the blind, 

 colorless side is now found on the right side of the fish, the left side 

 being the chromatic side. This species, as compared with the dex- 

 tral species, is remarkable for the greater development of the pig- 

 ment cells, figured on Pis. III. and IV. The young Flounder (PI. 

 VI. fig. 7), when not more than three-fourths inches long, is already 

 quite opaque, the whole colored side being thickly covered with minute 

 pigment cells : they extend also upon the dorsal and anal, in irregular 

 blotches, forming only in later stages the patterns which characterize 

 some of the species among our Flounders. It is not uncommon for a 

 peculiar pattern to appear quite early (see Pis. VII. and IX.). 



In the present species, the pigments of the dorsal and anal do not 

 appear before the stage figured on PI. VI. fig. 5. 



As will be seen, on an examination of the figures of PI. VI., the 

 earlier stages (Figs. 1-5) are readily recognized by the total absence 

 of pigment cells in the extremity of the caudal. This feature still 

 persists, in quite well-advanced individuals (PI. VI. figs. 6, 7, 8). 

 The tail, in this species, passes rapidly through the heterocercal stages, 

 and does not present the striking external resemblance to that of 

 Ganoids, so characteristic of the species figured in Pis. III. and IV. 



On PI. v., additional details have been given of the mode of trans- 

 fer of the eye from the one side to the other, — either the right eye to 

 the left side, or vice versa, — which, with the figures of the embryos, 

 on Pis. III., IV., VI., will show very clearly how the transfer is 

 accomplished, in the ordinary case of a dextral or sinistral Flounder. 



While still in the egg (PI. V. fig. 6), and for some time after hatch- 

 ing (PI. V. figs. 1, 2, 7, PI. III., PI. IV. fig. 1, PI. VI. figs. 1-4), the 

 eyes of the two sides are placed symmetrically on each side of the 

 longitudinal axis. The first change — and the process is identical, 

 whether we take a riojht or a left Flounder — is the sliojht advance 

 towards the snout (PI, V. fig. 3) of the eye about to be transferred; 

 so that the transverse axis, passing through the pupil of the eyes, no 

 longer makes a right angle with the longitudinal axis. This move- 

 ment of translation is soon followed by a slight movement of rota- 

 tion ; so that, when the young fish is seen in profile, the eyes of the 

 two sides no longer appear in the same plane, — that on the blind side 

 being now slightly above and in advance of that on the colored side 

 (PI. IV. fig. 2, PI. V. fig. 5, PI. VI. fig. 5, PL IX. fig. 7). With 

 increasing age, the eye on the blind side rises higher and higher to- 

 wards the median longitudinal line of the head ; a larger and larger 

 part of this eye becoming visible from the colored side, where the 



