2 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
learn from careful preparations of specimens in transition stages whether 
there was merely a mechanical twisting of the facial region in an other- 
wise normal fish, or a more elaborate rearrangement of the parts with 
reference to each other, and especially whether any histological changes 
accompany the more obvious external modifications. 
II. Material. 
The most of my work has been on the so-called winter flounder 
(Pseudopleuronectes americanus Walbaum), a dextral flatfish, but I 
have also used for the sake of comparison a sinistral species, the 
sand-dab (Bothus maculatus Mitchill). | 
My material was all collected at Wood’s Hole, Mass., during the years 
1898 and 1899. I obtained a series of developing eggs and young 
Pseudopleuronectes from the hatchery of the United States Fish Com- 
mission in April, 1898. Adult fishes can be taken by nets at any time 
through the year. The larval stages at or about the time of the 
migration of the eye are to be obtained during the month of June 
only. Early in the month only a few are at the point of assuming 
the adult position, and after June 20th, all the fish of this species taken 
were already metamorphosed. 
These larvee were caught by surface towing with a ooarse scrim tow- 
net near the wall of the “outer basin” of the U.S. F. C. wharf during 
the rising tide. They are most abundant on clear days when the wind 
is on shore and the tide comes in from the east. On very calm or very 
rough days they are not plentiful. My most successful skimmings 
were made early in June, and twice I obtained as many as 100 young 
fish during the inward flow of the current (3-4 hours). I was able to 
save a few of the young fish alive by frequently emptying the tow-net 
and placing the uninjured specimens in as pure water as possible. 
In the summer of 1898 the sand-dab larve were taken more abun- 
dantly than the winter flounders, while in 1899 the winter flounders 
were about ten times as numerous as the sand-dabs. 
I kept the young fish in the “outer basin” * in large lamp chimneys, 
1 The granite inclosure for the protection of smaller boats belonging to the 
United States Fish Commission is divided by projecting parts of the dock into the 
“inner” and “outer” basin. There are numerous openings in the stone walls to 
allow the free circulation of the water, and near one of these the float was 
moored, thus securing as nearly normal conditions of water and food as consistent 
with protection from violent wave action. 
