[13] RETARDING DEVELOPMENT OF SHAD EGGS. 807 



perature was 53.5o F. ; ou the 18th, 51.5° to 52° F. ; on the 19th, 

 53° to 53, jO F. ; development still normal. On the 20th the tem- 

 perature ranged from 53° to 54°; on the 21st, 55° to 55.5° F., and 

 about this time, or on the twelfth day, the eyes began to show the first 

 signs of pigmentation, becoming a shade darker than hitherto, verg- 

 ing toward brown. On the 22d the temperature of the water was 56° 

 falling to 55.5 o F. On this, the thirteenth day, a few began to hatch ; 

 the eyes were now fully pigmented and normal in their development. 

 On the 23d the temperature of the water was 55.5° to 54° F. On 

 the 24th the temperature was from 54° to 54.5° F. During the 

 23d and 24th days of April the hatching continued, most of the em- 

 bryos having ruptured their inclosing membranes on the 24th of April, 

 or the fifteenth day of incubation. On the 25th the temperature 

 ranged between 54.5° to 55° F., and on this date, or the sixteenth 

 day, a few of the ova still remained unhatched. On the 26th the tem- 

 perature was 55° F. ; all of the ova were now hatched, and no ab- 

 normalities of any sort were noticed. The embryos, however, were for 

 the most part lost, owing, as I think, to the circumstance that the water 

 was allowed to flow too rapidly and violently through the hatching-jar. 



The behavior of the hatching-jar was most admirable, but would 

 have been still better had there been a larger quantity of eggs put into 

 the apparatus. The most meritorious feature of the apparatus is the 

 almost entire non-development of the saprolegnious fungus, which 

 causes so great a mortality in some other forms of hatching contrivances 

 in which all of the ova are not in continual movement. The very grad- 

 ual, gentle, and continual rolling movement of the ova upon each other 

 in the jar apparently prevents the spores of the fungus from adhering. 

 The cleanliness of the apparatus is also to be commended, whereby the 

 use of skim-nets for cleaning is dispensed with, while the material 

 of which it is made — glass — enables one to watch the progress of devel- 

 opment very satisfactorily from the outside of the jar with a hand-glass 

 or ijocket lens of moderate power. 



On the seventeenth day of the experiment the hatched embryos were 

 in the condition of those normally developed at 70° to 75° F., the 

 yelk being ovoidal, clear, and plump. At the rate at which the develop- 

 ment progressed it would take five times as long to absorb the bulk of 

 the yelk of an embryo in a temperature of 53.75° F. as at 75° F., 

 or about twenty-five days. This period, added to the prolonged time of 

 incubation at 53.75° F., would cover a space of fort}' days, or more 

 than twice the time required to carry embryo shad to the farthest con- 

 fines of Europe. The probability therefore, is that we have exceeded 

 the lowest temperature practically required for this purpose, 55° F. 

 being a much more favorable and less dangerous temperature than that 

 prevailing during the successful experiment of which we have just 

 given a detailed account. 



