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VIII. On the Asymmetry of the Pleuronectidæ, as elucidated by an Examination of the 
Skeleton in the Turbot, Halibut, and Plaice. By Ramsay H. Traquaır, M.D., 
Demonstrator of Anatomy in the University of Edinburgh. | Communicated by Pro- 
fessor HUXLEY, F.R.S. & L.S. 
(Plates XXIX.-XXXII.) 
Read June 15th, 1865. 
Introduction. 
THAT both eyes of a Turbot, or of the Pleuronectidæ generally, are situated on 
one side of the head is a fact long interesting to naturalists in connexion with the 
peculiar habits of these animals. It also affords an interesting field for the anatomist 
and embryologist to ascertain what relation this asymmetry bears to the morphological 
plan of the fish-head in general. 
And indeed, if we merely look at the exterior of such a fish as the Turbot, the 
manner in which the transposition of the eyes has been effected is not very apparent. 
Itis, itis true, easy enough to imagine that the mesial line of the top of the head has been 
simply twisted over to one side, carrying with it the eye of the opposite. But the dorsal 
fin, which stretches all along the back in what is assuredly the mesial line of the fish, 
extends also uninterruptedly in the same straight line on to the head, beyond the eyes, 
and between the nostrils to nearly the end of the snout. If the mesial line of the top 
of the head has been twisted, why has such a distinctly median structure as the dorsal 
fin not undergone the same process at its cephalie extremity ? 
Or we may imagine that, in early development, one of the eyes has passed bodily 
through the head till it has reached that side where both are now found, and where it has 
formed for itself a new and anomalous orbit—a view which, it must be confessed, grates 
à little against most of our preeonceived morphological ideas. 
But from what we see on the outside of the fish we can only rashly speculate. It is 
only by means of anatomical and embryological research that we can gain an insight 
mto the true state of the case. 
Autenrieth is the oldest writer I have found who alludes to the subject anato 
“ Paper on the anatomy of the Plaice, published in the year 1800 *. His remarks on the 
osteology of the Plaice, however, are meagre ; and his theoretical conclusions must appear 
US now-a-days absurd, for he accounts in the following manner for the position of both 
eyes on the right side of the head. He says, “ The examination of the skeleton shows 
55 that the entire left side of the fore part of the cranium is, in reality, wanting, and 
mically, in 
und den Bau der Fische, hauptsäch- 
. 
Bemerkungen über den Bau der Scholle (Pleuronectes platessa) insbesondere, 
* Archiv für Zoologie und Zoo- 
lich i : : | 
to ees Skelets im Allgemeinen. Von Dr. J. H. F. Autenrieth. — M" 
mie, Theil i 1800, S. 47 et seq. 
VOL, XX, ei 
