806 REPOET OF COMMISSIONER OF FISH AND FISHERIES. [12] 



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

 may so call it, as iudicated 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 possible 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. Dui'ing 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 tbe 

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

 the casein 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 ap- 

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

 shad-ova develop normally was 49.5° F., as recorded in my report of 

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

 embryos which are the subject of this paper was any abnormality ob- 

 served in the development of the eyes or optic vesicles. 



Now for the history of the progress of the experiment and the ova. 

 The latter were taken at one of the Potomac stations organized upon 

 the plan proposed by Colonel McDonald. They were impregnated on 

 the 9th of April at 7 p. ra., and brought to the Armory on trays and 

 spread out on damp cloths by Spawntaker Jones. They were i>laced 

 in one of the McDonald jars on the morning of the 10th of April, but, un- 

 fortunately for the fullest fruition of our hopes, during the night, ow- 

 ing to an accidental occurrence or to the meddlesomeness of some irre- 

 sponsible busy-body, too large a supply of water was turned on, caus- 

 ing the largest proportion of the eggs to be thrown out by way of the 

 escape-pipe of the jar. What were then left, amounting to probably 

 two or three thousand, had to suffice for the material for this account of 

 their development. 



On the 11th of April the temperature of the water was 57° F. It 

 had been about the same or a little lower on the 9th and 10th 5 the water 

 of the Potomac, from which they were obtained at Ferry Landing, was 

 on those dates as low at 48° F. On the 12th the thermometer in- 

 dicated a temperature in the hatching apparatus ranging from 50° 

 to 51.50 JF. On the 13th the temperature ranged from 51° to 52° F. 

 This was the fourth day, and sketches taken from the eggs at this 

 time showed that the blastoderm was just about to close, a condition or- 

 dinarily attained in a temperature of 74° F. in somewhat less than twenty- 

 four hours. On the 14th of Ajml the temperature was 52° to 54° F. ; 

 on the 15th, 53° Fahr. ; on this, the sixth day, the tail began to bud out. 

 On the 16th tbe temperature was the same as on the previous day, and 

 the tail had by this time, the seventh day, grown to about one-third 

 the length of that of the just-hatched embryo. On the 17th, the tern- 



