188 NATURAL HISTORY SOCIETY OF DUBLIN. 
phalus, and in Trigla aspera ; seven in Mugil; eight in Trigla hirudo ; 
ten in Acanthurus chirurgus, and more numerous in the Herring, 
Trout, Coryphena, and Salmon. In the Cod they rise one step in 
complexity, and branch, as they do likewise in the Haddock and Mer- 
lan. In the Swordfish and Xiphias this branching is carried to a 
greater degree, and the ramifying ceca are united by lax areolar tissue, 
so as to make a solid glandular organ: these ceca open by two ducts 
into the duodenum. The nature of this structure, which has been de- 
scribed by Rosenthal,* and by Schellhammer,} was correctly stated by 
Redi, who describes it as a pancreas. In Acipenser it has three ducts, 
and iseven more solid than in Xiphias, while in the true Sharks it be- 
comes firm, glandular, and typical. 
THURSDAY, MAY 7, 1868. 
Read the minutes of previous meeting, which were signed. 
Rogpert CatweEtt, Esq., M. R.I. A., in the chair. 
A paper was then read, of which the following is an abstract :— 
On THE CRANIUM OF PSETTODES, AND ON A CASE OF Duplex Matrorma- 
TION IN PuatEssa FLESUS. By R. H. Traqvarr, M. D., Professor of 
Zoology, Royal College of Science, for Ireland. 
THE Professor pointed out that in Psettodes erumei, from the 
Indian seas, the greater part of the external boundary of the orbit con- 
taining the eye of the blind side is formed, not by a bone of the cranium 
proper, but by an intercalated suborbital. Psettodes is remarkable as 
being the most symmetrical genus of flat fishes as yet known—the 
upper eye, or eye of the blind side, being situated nearly on the top of 
the head, while the dorsal fin stops short a little before the posterior 
margin of the orbit. Dr. Traquair next described a remarkable case 
of arrested development occurring in Pleuronectes flesus, the common 
flounder. Malformed Pleurcnectide are common enough, in which the 
passage of the eye of the blind side has become arrested when it has 
reached the middle line of the top of the head, the anterior ray of the 
dorsal fin projecting then above the eye on a pointed process. But in 
this remarkable case the eye in question still remained on its own side, 
though placed on a higher level than its fellow. In consequence of 
this arrest of development, the bones of the frontal region of the skull 
differed considerably from those of the normal flounder, and resembled 
more those of the symmetrical fish, the interocular bar of the cranium 
being comparatively broad, nearly straight, and formed by processes 
from both frontal bones. No special bony orbit was formed to contain 
the eye thus arrested in its transit, showing that the closing in of this 
orbit is a secondary phenomenon consequent on the distortion of the 
* “ Abhandlungen aus dem Gebiete der Anat. Phys. u. Path. 1824,’ p. 79. 
t ‘* Anat. Xiphiz,” Hamburgh, p. 13. 
<4 
a 
