Dr. Davy on the Vitality of the Ova of the Salmonidse. 423 



have been much the same throughout England, When exammed, 

 eleven of the ova immediately became opaque on immersion in water. 

 In the other eleven there was no loss of transparency, and in these, 

 under the microscope, the circulation was found active. Those 

 which had become opaque were placed in a pretty strong solution of 

 common salt, by which their transparency was restored, the saline 

 solution dissolving the coagulum. Now examined, no traces of 

 development could be detected under the microscope in any one of 

 them, — showing that they had been dead before they were sent away. 



On the following day, the 18th of December, the eleven transpa- 

 rent ova were repacked, and again sent the same distance. They 

 came back on the 22nd; they retained then their transparency; 

 placed in water, a feeble circulation was to be seen in two under the 

 microscope ; in nine the blood-corpuscles had ceased to flow ; these 

 became opaque. Of the two in which the circulation was perceptible, 

 one was hatched on the 28th of December ; the young fish in the 

 other died, it would appear, in the act of breaking the membrane, its 

 head, on the 29th, having been found protruding, but the heart's 

 action stopped. 



The fifth experiment was made on the 26th of December. Ten 

 ova, in which the circulation was active, and the fcetus in each well 

 advanced, were sent off on the day mentioned, and returned on the 

 31st. The weather, during the whole time, was mild, the frost 

 having ceased. When opened, the ova were all found hatched, and 

 the young fish dead, as might have been expected. When put into 

 water, not one of them showed any signs of remaining vitality; they 

 were all examined under the microscope. 



The sixth and last experiment was made on the 6th of January. 

 Six ova, in each of which the circulation was vigorous, were put into 

 a glass tube of one cubic inch and a half capacity, with water to the 

 height of about I '4 cubic inch, the remaining space, after closure by 

 a cork, being filled with air. The intention was to try the effects of 

 conveyance to a distance on these ova in water with a small quantity 

 of air. Owing to a mistake, they were not forwarded. Examined 

 on the following day, five ova were found hatched, the young fish 

 dead ; in the one ovum remaining unhatched, the foetus was alive, 

 the circulation active ; on the 9th it burst its shell ; the young fish 

 was vigorous. 



As I could not with any certainty determine, at the time the ex- 

 periments were commenced, what eggs were impregnated and alive, 

 and what were not, I had at the beginning thirty ova taken indis- 

 criminately from the common stock, and put apart in a glass vessel, 

 the water in which was also changed daily. Of this number, seven 

 were found in progress of development on the 14th of December, or 

 23 per cent. ; the rest had become opaque. One of the seven was 

 hatched on the 31st of December, the others in succession, tbe last 

 on the 8th of January. 



Further to arrive at a proximate average of the proportion of im- 

 pregnated and unimpregnated ova, or living and dead, on the 14th 



