422 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



ADOITIOIVAr. OBSERVATIONS ON THE: RETARDATION OF THE DE. 

 VELOPMENT OF THE OVA OF THE SHAD. 



BY JOHN A. KIOEB. 



The following- data supplement and confirm in a somewhat remark- 

 able manner the arguments put forth by tbe writer in an article on the 

 retardation of the development of the eggs of the shad, iJublished in this 

 Bulletin, pp. 177-190, 1881. The facts there recorded were the results of 

 experiments carried out with the help of apparatus specially designed 

 to artificially lower the temj)erature of either the air or water in which 

 the eggs were hatched. Tbe value of the present series of observations 

 depends entirely upon the fact that no artificial means were resorted to 

 for tbe purpose of lowering tbe temperature, but that the eggs experi, 

 meuted upon, obtained, as they were, as early as the 9th day of April- 

 were, in consequence of tbe then i)revailing low temperature of the water, 

 subjected to no extraordinary or artificial condition arising from the use 

 of a complex water-or air-cooling apj)aratus. The temperature of the 

 water of the Potomac during the progress of the incubation of the eggs 

 in question was at times as low as 48° Fahr., but as a rule the water 

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

 exjieriment, fluctuated only between 50° and 56° Fahr., and even then 

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

 was rarely more than 1° Fahr. There was a gradual but very slight rise 

 in tbe temj)erature of the water from the beginning to the end of the 

 experiment, which covered seventeen days. This gradual rise was cov- 

 ered by six or seven degrees Fahrenheit, as already stated. The average 

 temperature of the water for the whole period was 53f o Fahr., which, 

 as we see, was only a little above the "danger point," 52° Fahr., if we 

 may so call it, as indicated by my observations made in association 

 with Messrs. McDonald and Clark last year. The results of this experi- 

 ment have shown us that it is i^ossible to retard the development of 

 shad ova so as to prolong the period of incubation for a period five 

 times that normally occupied in the process in the height of the spawn- 

 ing season, or for almost fifteen days. During my somewhat extended 

 observations on the eggs of this species, no such length of time of in- 

 cubation has been recorded, nor has any one, to the best of my knowl- 

 edge, recorded the fact that under such conditions of temperature the 

 progress of the evolution of the embryo was perfectly normal, as was 

 the case in the instance now to be described. Several persons have in- 

 sisted that shad ova developing in too low a temperature would be found 

 to be imperfect, especially the eyes, which, it was said, did not appar- 

 ently develop at all. The lowest temperature in which I have seen 

 shad ova develop normally was 490.5 Fahr., as recorded in my report of 

 the experiments during the spring of 1881. Neither in those nor in the 



