100 The First Food of the Comynon White -Fish. 



with water from a spring, wliicli 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 



