[11] RETARDING DEVELOPMENT OF SHAD EGGS. 805 



because sudden meteorological changes, such as we sometimes experi- 

 ence in this latitude, would influence the working of the apparatus. 

 The best regulator would probably be a faithful attendant. The con- 

 trol of the temperature of the water flowing through coils surrounded 

 with ice is, in the light of experience, a comparatively easy matter, as 

 it has been found that in a coil of a given length the fluctuation in the 

 temperature will not vary more than three or four degrees, if a little at- 

 tention is bestowed in regulating the flow and keeping a good supj)ly 

 of ice packed around the coils. 



The prevention of leakage or loss of water from the apparatus would 

 be entirely overcome, both on board cars and steamships, by the adoption 

 of the closed glass hatching-jars, of various forms, devised by Colonel 

 McDonald. They appear to be cheap, and are very economical of room. 

 There can therefore be no objection to the introduction of the apparatus 

 into vessels and railway express cars on the score that it makes objec- 

 tionable slop and slush on the floors or decks. 



The foregoing, it appears to me, is an approximate solution of the 

 problems which we set out to answer. Whether we are right another 

 season's work ought to enable us to decide practically and finally, as we 

 can now take up the subject intelligently. The preliminary experimental 

 work has been completed. 



LATER OBSERVATIONS ON THE RETARDATION OF THE DEVELOPMENT 

 OF THE OVA OF THE SHAD. 



The following data sui)plemeut and confirm in a somewhat remark- 

 able manner the arguments put forth above. The facts there recorded 

 were the results of experiments carried out with the help of apparatus 

 specially designed to artificially lower the temperature of either the air 

 or water in which the eggs were hatched. The value of the present series 

 of observations depends entirely upon the fact that no artificial means 

 were resorted to for the purpose of lowering the temperature, but that 

 the eggs experimented upon, obtained, as they were, as early as the 9th 

 of April, were, in consequence of the then i^re vailing low temperature 

 of the water, subjected to no extraordinary or artificial condition arising 

 from the use of a complex water or air cooling apparatus. The temper- 

 ature of the water of the Potomac during the progress of the incubation 

 of the eggs in question was at times as low as 48° F., but as a rule the 

 water then in use in the McDonald hatching-jars, the apparatus utilized 

 in the experiment, fluctuated only between 50° and 50° F., and even 

 then very gradually, as the variation during any one period of twelve 

 hours was rarely more than 1° F. There was a gradual but very 

 slight rise in the temperature of the water from the beginning to the 

 end of the experiment, which covered seventeen days. This grad- 

 ual rise was covered by 6° or 7° F., as already stated. The average 

 temperature of the water for the whole period was 53fo F., which. 



