844 PROFESSOR W. C. MINTOSH AND MR E. E. PRINCE ON 
tion thus produced caused the flounder to dart about with great energy.* Young 
flounders, colourless, and of glassy transparency, rapidly develop pigment in the laboratory. 
The remarkable appearance of the tail (opisthure, RypEr), with its marginal fringe 
of rays before any change takes place in the position of the eyes, recalls the condition of 
the tail in such extinet forms as Kriver’s Graphiurus callopterus, in which, however, 
the vertebral column is prolonged in a straight line, instead of being bent up, and the 
ordinary caudal rays pass dorsally and ventrally from it. Kunrr’s form referred to, came 
from the bituminous shale of Raibl in Kirmarthen.t 
The young flounders proceed a considerable distance up the fresh-water stream at a 
stage somewhat older than the foregoing. 
If the forms observed in the muddy sand of the tidal pools, and also caught in the 
mid-water net in the bay in April, are the young of the season, their growth is re- 
markably rapid, even granting a much earlier period for spawning than has been observed 
at St Andrews (April). 
During April, May, and June, very small specimens of the flounder occur at St 
Andrews in the shallow rock-pools, containing stunted Algze (Ceramiwm and other 
forms), with a slight coating of grey mud. From their translucency the young fishes 
are invisible, especially on the greyish silt, in which they are often partially immersed, 
and, as ALex. AGassiz noticed, the two prominent eyes alone attract attention, while the 
bodies of the fishes themselves cannot be seen. They are elongated and slender, about 
12 mm. long and 5°5 mm. in total breadth at the widest part. At this stage the true 
pleuronectid features have been assumed. They swim with the dorso-ventral line horizontal 
(the right side uppermost), and dart about with rapidity, frequently in confinement leaping 
over the margin of the vessel. They are fond of attaching themselves to the perpen- 
dicular sides of a glass vessel, as if their left (white) side had a sucker, but the adhesion 
is simply due to the muscular action of the whole surface. Both eyes are visible from 
the right side, though the left eye is more or less lateral in position, or capable of looking 
slightly downward. In company with them, plaice of the same length occur, being 
distinguishable as broader and thinner fish, with the left eye not so far to the right, 
and the ventrals as mere rudiments, while those of the flounder are well formed. 
The flounder is apparently a considerably older fish, and its left side is quite white, 
while in the plaice the pigments formerly mentioned occur. The coloration of the 
flounder varies rapidly, and though, when first captured, their anatomy is readily ob- 
served from their great translucency, yet, as indicated, a few days’ exposure to an in- 
creased amount of light, from absence of shelter in the tanks of the laboratory, causes 
such a development of pigment, that they are useless as transparent objects. The blackish 
pigment-spots persisting after preservation, present a close approach to those in the young 
plaice of the same size. Thus along the dorsal body-line five pigment-spots occur, and 
four along the ventral line, almost the same number as in the former species. The general 
* The food of these flounders consists of young Gammari and similar Crustaceans. 
+ Sitzungsbr. der K, Akad. Wien. Naturwiss., Bd, 53 and 54, 1866, p. 155, Taf. i. fig. 1. 
