380 Prof. J. C. Schiodte on the Development of 



men last described, on account of the change which is observed 

 in the position of the left eye, which is now placed not only 

 above the right eye, but at the same time a little behind it. 

 The left eye is entirely transferred to the right side, though it 

 stands so high on this side that its pigment, dimly shining 

 through the skin, can still be seen from the left side as a small 

 dark border. A striking evidence of its having receded further 

 back is afforded by the fact that the first ray of the dorsal fin 

 in this specimen stands so far forward, in comparison with the 

 eye, that it is on a level with the middle of its left margin, 

 whilst the third ray occupies the place relatively to the eye 

 which in the former specimen is occupied by the first ray. 



The specimens of young Hippoglossus pinguis which I 

 have before me present a similar progressive development. 

 The smaller is 57 millims. long. The outlines of all the super- 

 ficial parts of the skull are distinctly seen through the skin, as 

 well as the branches of the muciparous canal and their nume- 

 rous ducts. The left eye is placed at the top of the head, so 

 much inclined to the left (blind) side, that from the right side 

 the iris is only partly visible, and the pupil altogether in visible ; 

 it is 25laced straight in front of and close to the dorsal fin, which 

 points alongside the right margin of the pupil. On the head of 

 a second specimen, which is nearly twice as large (lOOmillims.) 

 the ducts of the muciparous canals are evidently more nume- 

 rous, and the infraorbital branch on the left (blind) side, which 

 on the smaller specimen appears curved, is here almost straight. 

 It has got space to grow straighter ; for on this specimen the 

 left eye has moved across the head so much that it now inclines 

 as much to the right side as formerly to the left ; and whilst 

 in the smaller specimen it stood nearly straight before the 

 dorsal fin, the latter would, if prolonged in the larger speci- 

 men, cross the eye just inside its left margin. That the 

 eye is under pressure, wedged in between the interspinous 

 part of the dorsal fin and the anterior frontal bones, is evident 

 from an indenture in its outline on the posterior margin ; and 

 this pressure evidently cannot cease till the eye, gliding still 

 further to the right, has got clear of the dorsal fin. 



In order to explain how the upper eye of the Pleuronectidse 

 comes into that position relatively to the dorsal fin which it 

 occupies in the adults, naturalists have had recourse to the 

 hypothesis that the dorsal fin prolongs itself in a forward 

 direction when the upper eye, by the torsion of the head, has 

 come into its final place. This hypothesis was first proposed 

 by Van Beneden (Ann. Sc. Nat. sdr. 3. t. xx., " Note sur la 

 Symetrie des PoissonsP/e?<rowectes dans leur jeune age,"p.342), 

 and has been adopted also by Dr. Traquair,in his exhaustive and 



