374 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



form of apparatus that ingenuity could devise was used without success, 

 and unless the failure is to be attributed to the low temperature of water 

 prevailing during the course of the experiments (the range of tempera- 

 ture being 50° or below), I am utterly at a loss to explain our want of 

 success. 



The shad eggs after being taken were held at Fort Washington Station 

 from 12 to 36 hours, and then were forwarded by the steamer Corcoran, 

 in charge of a special messenger, to Central Station, where they were 

 hatched, and from which they were distributed by car and messenger 

 service. , 



The total number of eggs produced at the collecting station at Fort. 

 Washington, as measured at the station, was 22,576,000. Of these 

 21,019,000 were forwarded to Central Station, and the rest, yielding 

 1,000,000 fry, were hatched out at the station and planted in the Potomac 

 at the mouth of the Piscataway Elver. Of the entire number sent to 

 Washington 16,536,000 reached the station in good condition, and yielded 

 14,791,000 shad fry for distribution. 



A separate record was kept of each lot of eggs, so as to furnish a 

 complete history of it from the time the eggs were taken until they 

 were distributed from Central Station. The detailed record will be 

 found in Table IV. The time and temperature data can be relied upon 

 as accurate only in the case of eggs furnished from the commission 

 seine. 



By reference to this table it will be seen that under precisely the same 

 conditions of temperature, so far as recorded, the period of time from 

 impregnation to hatching varies from a few hours to several days. It 

 is evident that the period of incubation does not simply vary inversely 

 to the temperature as indicated by the thermometer under which incu- 

 bation proceeds, as I have been led to conclude from observations here- 

 tofore made. 



The rate of development is not determined by the temperature at 

 which impregnation takes place, since we find considerable differences 

 in the period of incubation when the temperature of impregnation is 

 precisely the same. 



We know that in damp and cloudy weather the rate of development 

 is slowed down, that in direct sunlight it receives marked acceleration, 

 and to a less degree by reflected light in clear, bright weather. After 

 all, this may be the indirect effect of increased temperature, since 

 either the direct or reflected heat rays would pass through the flowing 

 water without producing any sensible rise of temperature in it, but 

 would be absorbed by the eggs and accelerate their development just as 

 would result if the temperature of the water itself were to rise. 



The earlier runs of shad habitually spawn in a lower temperature 

 than those that come later in the season. It may, therefore, well be 

 that a difference in the rate of development of different lots of eggs may 

 come by inheritance. 



