REPORT OF COMMISSIONER OF FISH AND FISHERIES. LXXIII 



height of the season. It may be stated that no twin discs were found 

 among the other lots examined, although after the above experience it 

 had been confidently expected to find them. Never before, however, 

 has a twin disc been observed in a whitefish egg, and only three were 

 found this season outside of the lot under consideration; neither have 

 twins or double-headed monstrosities been found common among the 

 whitefish fry, though they are common among the lake trout. 



The development of this lot of eggs was watched with much interest, 

 but on January 10, when the embryos began to form, not a single twin 

 or double-headed one could be found. It was observed, however, that 

 20 per cent of the eggs were far behind the rest in point of develop- 

 ment and, though apparently alive and healthy, there was no sign of 

 embryotic formation. This went on until January 26, when two well- 

 defined double-headed embryos were discovered. From this on they 

 were found in numbers, though very few of them had two perfect heads, 

 and there were no well-marked twins — that is bodies entirely separated 

 except by their attachment to the yolk-sac, as is so common with trout. 

 Most of the monstrosities had one normal and one abnormal head. It 

 is worthy of note that the perfect head was, without a single exception, 

 on the left side, and where both were abnormal the left one was the 

 better of the two, as will be noted in the accompanying micrographs. 



Since writing the above Superintendent Stranahan has learned, by 

 consultation with Prof. Jacob Eeighard, of the University of Michigan, 

 that in his opinion the large number of abnormalities found among 

 these eggs was caused by their being held long past the normal time of 

 deposit. His experience showed that this is likely to be the case with 

 amphibians held in confinement. This may furnish the reason why late 

 eggs show more monstrosities than those taken early in the season. 



The penning of whitefish near the station this season has afforded 

 exceptional opportunities for experiment with the fertilization and 

 development of the ova, and considerable attention has been paid to 

 the determination of how long milt will retain its vitality after being 

 mixed with water. On December 4 a quantity of spawn, just as it was 

 taken from the fish, was brought to the station, and a small quantity 

 placed in each of 10 perfectly dry, clean pans, which were set in run- 

 ning water at a temperature of 36°. The milt of three males brought 

 alive to the station in a tub of watei was taken in a dry pan, care 

 being exercised that no water dripped from the fishes into the pan. 

 Water was then added, and a portion poured into one of the pans 

 containing eggs, numbered 0. In a quarter of a minute another 

 portion was poured into the pan numbered 1, and so on to the finish. 

 After each lot had stood one minute the eggs were washed and placed 

 in kegs in running water, with numbers to designate each lot. On 

 December 5, the eggs, being well segmented, were carefully examined 

 under the microscope, to determine the percentage of impregnation. 

 In each case those with ruptured sacs, or those destitute of germinal 

 disks were not taken into account, the object being to determine the 

 percentage of impregnation at the different periods. 



