THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[THIRD SERIES.] 

 No. 89. MAY 1865. 



XXXVI. — Notes on Prof. Steenstrup's Views on the Obliquity of 

 Flounders'^. By Prof. Wyville Thomson, LL.D., F.R.S.E., 

 M.R.I.A., F.G.S. 



[Plate XVIII.] 



Any contribution from the pen of the accomplished author of 

 the 'Alternation of Generations^ must be welcome; and the 

 present communication " On the Migration of the upper Eye of 

 Flounders, across, through the Head, from the blind side to the 

 eye-side,^^ almost vies in novelty with the author's earlier me- 

 moir. The original paper is in Danish, and consequently a 

 sealed book to most English students ; and many interesting 

 points are omitted in Prof. Steenstrup's French letter to M. 

 Milne-Edwards. We shall therefore commence with a tolerably 

 full abstract of the communication to the Danish Academy, 

 reserving any remarks we may have to offer until the reader is 

 in full possession of the author's views. 



I. 



The general fact of the obliquity of the Pleuronectidse is well 

 known. All Flounders have a high compressed body, whose 

 two sides are unequally developed. This want of symmetry is 

 universally accompanied by another peculiarity : both eyes are 

 brought round to one side of the head, so that the fish acquires 

 an eye side and a blind side. The former is coloured and turned 

 upwards towards the light ; the latter is colourless or white, and 

 turned downwards in motion or rest. The fish moves or lies 



* J. Japetus Sm. Steenstrup : — ' Om Skjaevheden hos Flynderne, og 

 navnlig om Vandringen af det ovre Oie fra Blindsidea til Oiesiden tvers 

 igjennend Hovedet.' Kjobenhavn, 1864. Saerskilt Aftryk af Oversigt over 

 d. K. D. Vid. Selsk. Forhandl. i Nov. 1863. 



" Observations sur le Developpement des Pleuronectes." Par M. Steen- 

 strup. (Annales des Sciences Naturelles, Novembre 1864.) 



Ann. ^ Mag, N, Hist. Ser. 3. Vol. xv. 24 



