[5J THE FIRST FOOD OF THE COMMON WHITEFISH. 775 



ri.\ . The oidiuary ruu^^e of teuiperature iu the tauk was from 35° to 

 390. These fishes were fed daily with a paste made by griuding small 

 amphipod crustaceans (Gammarus) in a mortar. 



The second lot, hatched January 20, was kept, unfed, in a perforated 

 tin box, iu a rivulet flowing from a spring, about 60 feet from its source. 

 The water had a uniform temperature of 47°. 



Those in the spring, being in warmer water than the otliers, develop- 

 ed 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 appropriate. 



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 ab- 

 sorbed in most of the lot, but in those most advanced was represented 

 by an oil globule back of the head. Tlie pectoral fins were well devel- 

 oped, but no trace of the ventrals had as yet appeared. The single 

 median fin extended well in fi^ont of the vent, and forwards on the back 

 nearly to the head. The opercles did not fully cover the gills. The 

 most highly developed specimens — those whose gill-sacs had nearly- dis- 

 appeared — had, at a short distance on either side of the symphysis of 

 the lower jaw, a sharji, 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, direct- 

 ed almost exactly inwards. The upper jaw was, however, wholl}^ tooth- 

 less. 



These fishes were all i^assed under the microscope, after having been 

 rendered transparent, but only four of them contained anything what- 

 everj three a little dirt, and the fourth a minute fragment of the crust 

 of the Gammarus, with which they had been fed. 



Of one hundred and eleven specimens received February 17, seven- 

 teen had taken food. I dissected nine of these and found fragments of 

 Gammarus and nothing else. Ninety specimens from the same lot were 

 examined February 25, and food was found in fourteen. Four of these 

 had eaten Gammarus fragments; two, larvte of gnats; one, a small 

 Gypris, and eight contained small fragments of the leaves and stems of 

 vascular plants, including a bit of a netted- veined leaf and a little i)iece 

 of pine wood. Thirty-nine specimens, the last of the lot, were received 

 March 15, and food was found in fourteen. I dissected nine of tliese, 

 finding fragments of Gammarus in four, a larva of a gnat, a Chironomus 

 larva, a larva of some undetermined fly, a minute vegetable fragment, 

 a Cyclops, a Cypris, and an undetermined Eutomostracau each in one. 

 Three hundred and forty fry from the hatching-house were examined in 

 all, in forty-seven of which (fourteen per cent.) more or less food was 

 discernible. Of the thirty -five dissected, eighteen had eaten Gammarus 



