On the Development of the Pleuroneetidce. 215 



Wednesday, January 25, 1865.— T. Strethill Wright, M.D., 

 President, in the Chair. 



Rev. James Brodie, Monimail, Fife, was elected a non-resident member 

 of the Society. 



, The following Donations to the Library were laid on the table, and 

 thanks were voted to the Donors : — 



1. (1.) Transactions of the Zoological Society of London. Vol. IV., 

 Part 7, Section II., 1862 ; also Vol. V., Part 3, 1864. (2.) Proceed- 

 ings of the Zoological Society of London, 1861. Part 3, June-December ; 

 also Parts 1, 2, and 3, January-December 1863. — From the Society. 

 2. (1.) Transactions of the Royal Society of Edinburgh. Vol. XXIII., 

 Part 2, Session 1862-63. (2.) Proceedings of the Royal Society of 

 Edinburgh, Session 1862-63. — From the Society. 



The following Communications were read : — 



I. Observations on the Development of the Pleuronectidw . By Ramsay 

 H. Traquair, M.D. 



That both eyes of a turbot, or of any of its congeners 

 {Pleuroneetidce) , are situated on one side of its head, is a 

 fact long interesting to naturalists, in connection with the 

 peculiar habits of those animals. It also affords an interest- 

 ing 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. It is true, it is easy to imagine that the 

 mesial line of the top of the head has been simply twisted 

 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 uninter- 

 ruptedly 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 middle line of head has been twisted, why 

 has such a distinctly median structure as the dorsal fin not 

 undergone the same process at its cephalic extremity ? 



Or we may imagine that in early development one of the 



