100 
The First Food of the Common White-Fish. 
with water from a spring, which had been cooled by exposure to 
the air in artificial ponds before entering* the hatchery, in order 
to retard the development of the fry. The ordinary range of 
temperature in the tank, was from thirty-five to thirty-nine de- 
grees. These fishes were fed daily with a paste made by grinding 
small amphipod crustaceans (Gammarus) in a mortar. 
The second lot, hatched January 20, was kept, unfed, in a per- 
forated tin box, in a rivulet flowing from a spring, about sixty feet 
from its source. The water had a uniform temperature of forty- 
seven degrees. 
Those in the spring being in warmer water than the others, de- 
veloped much more rapidly, and it was believed that the character 
and source of this water was such as to furnish them at least a 
small supply of such food as young fishes are accustomed to ap- 
propriate. 
Ninety specimens were received from the hatchery February 9, 
at which time they were three weeks old. They were thirteen 
mm. (half an inch) in length by one in depth. The egg-sac was but 
partially absorbed in most of the lot, but in those most advanced 
was represented by an oil globule back of the head. The pectoral 
fins were well developed, but no trace of the ventrals had as yet 
appeared. The single median fin extended well in front of the 
vent, and forwards on the back nearly to the head. The opercles 
did not fully cover the gills. The most highly developed spec- 
imens — those whose gill-sacs had nearly disappeared — had, at a 
short distance on either side of the symphysis of the lower jaw, 
a sharp, strong, raptatorial tooth, curved backwards and slightly 
inwards. The base of this tooth was very broad, and the point 
acute and slender. At a point behind each of these teeth about 
half their distance from each other, was a second much smaller 
tooth, directed almost exactly inwards. The upper jaw was, how- 
ever, wholly toothless. 
These fishes were all passed under the microscope, after having 
been rendered transparent, but only four of them contained any- 
thing whatever; three a little dirt, and the fourth a minute frag- 
ment of the crust of the Gammarus, with which they had been 
fed. 
Of one hundred and eleven specimens received February 17, 
seventeen had taken food. I dissected nine of these and found 
