‘the Position of the Eyes in Pleuronectide. ~ 381 
instructive treatise ‘ On the Asymmetry of the Pleuronectide’”’ 
(Trans. Linn. Soc. 1866, vol. xxv. p. 263)*. The fact, however, 
that the young fish, at least those examined by me, possess 
the same number of rays in the dorsal fin as the adults, would 
in any case render this theory very doubtful, even if it had 
not now been proved by the observations above detailed 
that the eye of the blind side does not only glide over from 
ats own to the eye-side of the fish, but, when arrived here, it 
recedes a little along the dorsal fin. It is consequently the 
eye which moves round the anterior end of the fin, not the 
fin that prolongs itself past the eye. A comparison between 
different specimens of the same species shows that the change 
of place is rather a slow process. On the head of the young 
Lth. barbatus above referred to, which is 18 millims. long, the 
eye is still quite in front of the fin; on another specimen 
of the same species which I have before me, and which is 
45 millims. long, the centre of the eye is on a level with 
the second and third ray of the fin; on a third specimen, 
90 millims. long, the eye is on a level with the third and 
fourth rays, and on a fourth specimen, 115 millims. long, it 
has receded as far as the fourth and fifth rays. 
The total length of the first-described young P. platessa was, 
as stated, 10 millims. including the caudal fin. If, then, we take 
into consideration the proportionally great size of the eggs of 
this species, which measure 2 millims. in diameter, as well as 
the fact that the fish-embryo is, as it were, rolled up inside 
the ovum, it becomes clear that the specimen in question must 
have been caught not many days after having left the egg. 
Even allowing a margin for more rapid growth during the 
first days after hatching, it must be conceded, on comparing 
the three specimens above described, respectively 10 millims., 
_ * Dr. Traquair ascribes to Fr. Rosenthal the opinion that the upper 
eye of the flounders attains to its anomalous final position by passing 
under the dorsal fin right through the head ; but, although Rosenthal’s 
expressions (Ichthyotomische Tafeln, ii. 3, Berlin, 1821, 4. p. 5) are vague 
enough, and may be so interpreted, I think that he may equally well be 
supposed to have intended only, by a sort of figure of speech, to illustrate 
the peculiarity of the flounder-skull. The idea that a highly complicated 
organ, after having attained its full development, should loosen itself 
from the ground out of which it has grown, wander about amongst other 
utterly different organs of the body—nay, even go right through the 
body of the animal, in order to turn up again on the other side and 
take root there—this idea is one which scientific zoolegy now-a-days can 
only yer aside as a curiosity. I therefore think it due to the memory of 
so able an anatomist as Rosenthal that such a crude opinion should not 
___ be ascribed to him except on more cogent grounds, although the plate 
in the explanation of which the expressions in question occur was pub- 
lished as early as 1821—that is, only a few years after the foundation of 
comparative anatomy by Bichat. ) 
