WILLIAMS: MIGRATION OF EYE IN PSEUDOPLEURONECTES. 9 
peculiar fish described by Schiddte was an example of an intermediate 
method. 
Only two other descriptions of intermediate methods of eye-transition 
need be noticed. Ehrenbaum (’96) has discussed, among other points, 
metamorphosis in the flatfishes of the German Ocean. Stages of the 
larvee of the commoner species in which the eye passes around the head 
are given. In the larva of Arnoglossus laterna, which strongly resembles 
the so-called Plagusize, the dorsal fin extends to the nostril while the 
fish is yet symmetrical, so that the eye must pass under the dorsal fin as 
in Plagusia. The prolongation of the dorsal fin to the nasal pit and the 
position of the right eye close to the lower margin of the fin (after 
migration) prove, in Ehrenbaum’s opinion, that the right eye is 
shoved through under the dorsal fin from the right to the left side. 
Recently a Japanese zodlogist, T. Nishikawa (’97), found a case 
where the dorsal fin extended along the head as far as the end of the 
snout in close contact with, but not fused to, the skin. There were no 
fin rays located in the eye region. The right eye passed through a slit 
between the fin and the head in one day, passing thus from one side 
completely to the other. Unfortunately the fish died, so that it is not 
known whether the fin would have fused later to the dorsal part of 
the head or not. 
2. DESCRIPTION OF STAGES. 
For convenience of description four stages of development may be 
recognized in Pseudopleuronectes americanus. 
Stage I., the recently hatched fish, is represented (Plate 1, Fig. 1) by , 
a specimen 3.5 mm. long and 12 days old. Owing to its wide dorsal 
and ventral fins being so transparent as to be scarcely visible, the 
living animal resembles, in its general appearance, a very minute 
pin with an elongated head. It is essentially symmetrical. I have 
sectioned the eggs as well as the young fish and find a close resem- 
blance to the figures given by Fullarton (’91) in his work on the develop- 
ment of the plaice, Pleuronectes platessa, which is the nearest European 
representative of our flatfish. His drawings, too, show the eyes to be 
symmetrical in position. There are few pigment cells in the body of 
an animal of this stage and they are arranged in much broken 
longitudinal lines. 
The largest of the recently hatched fishes are nearly as long as the 
smallest of the pelagic larvae (Stage II., Plate 1, Fig. 3), which were 
taken the first of June; but between the two there is a great difference 
