Dr. Davy on the Vitality of the Ova of the Salmonidse. 421 



that they became opaque in the course of twenty -four hours, all but 

 one, and that, some days after, underwent the same change, denoting 

 loss of vitality. 



The second experiment was made on the 10th of November. Six 

 ova were similarly exposed for two hours to a temperature rising 

 gradually from 70° to 78° ; the result was similar : on the following 

 day they were all found opaque. 



The third experiment was made on the 11th of November. The 

 same number of eggs were exposed for an hour to a temperature 

 falling from 70° to 69°. Two shortly became opaque ; four retained 

 their transparency during a month, though in reality dead, which 

 was denoted by their bearing no marks of development when seen 

 under the microscope, those ova which retained their vitality being 

 at that time well advanced. 



The fourth experiment was made on the 1st of December ; the ova, 

 the same number, were exposed to a temperature rising from 75i° to 

 78° for an hour and twenty-two minutes. Three became opaque, 

 other three retained their transparency and vitality, and in due time 

 were hatched, the first on the 31st of December, the last on the 7th 

 of January. 



The fifth experiment was made on the 13th of December. Six ova 

 were exposed for an hour and twenty-five minutes to a temperature 

 falling from 82°, which it was at the beginning, to 78°, which it was 

 at the end. Two became opaque ; in these no marks of progress 

 could be seen of development, thus indicating that they were dead at 

 the time of trial. Four remained transparent ; in these, under the 

 microscope, embryo-fish were seen with an active circulation of the 

 blood-corpuscles. One of them was hatched on the 31st of Decem- 

 ber ; one, the last, on the 6th of January. 



The sixth experiment was made on the 20th of December, on six 

 ova, containing living embryos. They were exposed for an hour and 

 twenty-eight minutes to a temperature of about 98°, and this during 

 the whole time. When taken out, they had not lost their trans- 

 parency, but in each the heart's action was arrested, and death was 

 the result : they all sooner or later became opaque, from the common 

 cause, the imbibition of water. 



The seventh experiment was made on the 21st of December, on six 

 ova, in which the circulation was distinct in the foetal fish. After 

 an exposure for an hour and five minutes to a temperature of 70° 

 rising to 82°, in five, on cooling, the circulation was found active ; 

 in one, stopped, which was dead ; two were hatched on the 5 th of 

 January ; three, the remainder, on the 7th of the same month. 



The eighth experiment was made on the 23rd of December, on six 

 ova, each containing a living foetus. They were exposed to a tem- 

 perature falling from 84° to 82° during an hour and twenty minutes. 

 Examined after the water had cooled, in one, the circulation was seen 

 pretty distinct ; in two, very feeble ; in three, the blood- corpuscles 

 appeared to be stagnant. Examined on the following day, the cir- 

 culation was seen active in all. One was hatched on the 5th of 

 January, the other five in the two following days. 



