46 GERTRUDE M. WHITE 



eggs is dependent upon the temperature of the water, varying 

 from about 125 days at 37° F. to about 50 days at 50° F. 



The experiments here described were performed in the Zo- 

 ological Laboratories of the University of Wisconsin. About 

 five hundred embryos were used, eggs being obtained at the 

 Madison Fish Hatchery, and brought to the laboratory in four 

 different batches, so that embryos of various stages could be 

 observed at the same time. The youngest stages were kept in 

 a wire tray in a trough of running water (from Lake Mendota) 

 while the older individuals were placed in glass dishes and set 

 in running water to keep them cool. About one hundred Rain- 

 bow Trout, Salmo irideus, of two different stages and a number 

 of young German Brown Trout, Salmo fario, which swam freely 

 in the trough, were kept under observation. 



During the experiments the temperature of the water ranged 

 from 5° C. to 10° C. Most of the experiments were performed 

 in a dark room, the temperature of which was usually about 

 19° to 20° C. The fish were handled with a feather or with a 

 spoon made of bent wire with netting stretched across it. Al- 

 though theie was a high rate of mortality (due to gas-bubble 

 disease, fungi, algae which crept into the gills, and persistent 

 handling), several of the Brook Trout survived during the whole 

 period. All experimental data refer to the Brook Trout unless 

 otherwise stated. 



This work was accomplished under the direction of Professor 

 A. S. Pearse, for whose helpful suggestions and encouragement 

 it gives me great pleasure to express my appreciation. 



B. EXPERIMENTS AND OBSERVATIONS 

 1. Hatching 



The egg of the Brook Trout is small and nearly colorless, 

 measuring about four millimeters in diameter. The embryo, 

 which is about three times as long as the diameter of the egg, 

 lies curled around its yolk sac with the tip of the tail beside 

 the head. The eyes and head are visible through the thin shell. 

 The hatching is initiated by movements starting at the head 

 and later extending through the whole length of the body, so 

 that the position of the embryo in the egg is somewhat changed. 

 Such movements continue at intervals, varying from a quarter 

 of a minute to an hour or more, until the shell is so strained 



