74 



T. NISHIKAWA. 



the rotation of the head, towards the dorsal side of it, and approached 

 more and more the hase of the dorsal fin ; eventually it passed into the 

 hole between the head and the anterior extension of the dorsal. 



snout. Thus it was evident that the hole in front of the base of the 

 dorsal was intended for the passage of the right eye, which travelled 

 around the dorsal surface of the head, from the right to the left side. 

 There occurred neither a new formation of the orbit for the right eye on 

 the left side nor the atrophy of the original orbit of the right eye on the 

 right side, as in the case of the Plagusia described by Agassiz.* 



The fish died on the evening of the next day, after the rotation of 

 the right eye was finished ; it had then many pigment-spots on the left 

 side, and the snout was produced backwards into a hook, covering the 

 mandible. The general characters of the young fish being still very 

 incomplete, it was not possible to identify it, but it is probable that it 

 belongs near the genus Plagusia. 



According to the observations of Agassiz, there are two different 

 modes of the passage of the eye in flat-fishes ; one of them is undergone 

 by a majority of species, such as Pleitronectes, Pseudorliombus, and 

 others. In this mode, the eye on the side which in the adult is blind, 

 travels round the dorsal side of the head, till it attains its final position, 



This stage is shown in fig. 2, which 

 was drawn at 10 : 30 P.M. of the same 

 day ; the anterior extension of the 

 dorsal fin has not yet united with the 

 head. The right eye then emerged 

 on the left side and moved towards 

 its final position. After this rota- 

 tion, there occurred a fusion of the 

 head and the anterior part of the dor- 

 sal fin, from the base towards the 



Fig. 2. 



* A. Agassiz.— On. the Young- Stages of same Osseous Fishes. II. Development of 

 the Flounders. Proa of the Amer. Acad. Arts & Sci., vol. XIV. IS78. 



