Dr. Davy ow the Vitality of the Ova of the Salmonidse. 307" 



-^ The ninth experiment was made on the 24th of December. Six ova 

 were exposed for two hours and four minutes to a temperature faUing 

 from 72° to 70°. Examined a quarter of an hour after, and before 

 the water was cold, the circulation was found vigorous in all. One 

 was hatched on the 2nd of January, the remainder between the. 5th; 

 and 8th. ikot-Br^ 



The tenth experiment, and the last of its kind that I have to 

 describe, was tnade on the 2nd of January. Six ova, in each of which 

 the circulation was distinct, were exposed for four hours to a tem-* 

 perature varying from 70° to 72° — ^the greater part of the time 72°. 

 Examined immediately on being taken out, the circulation was seen 

 uninterrupted in three, arrested in the other three. In three-quarters 

 of an hour, when the water had cooled nearly to the temperature of 

 the room, 55°, the circulation was found to be renewed in the latter. 

 In the interval, one of the former was hatched, and a vigorous fish 

 produced ; on the following morning four more had come forth, and 

 in the one remaining egg the foetal circulation was vigorous ; it was 

 hatched on the 4th of January. 



I beg now to pass to the other series of experiments referred to, 

 those in which trial of the vitality of the ova was made by sending 

 them to a distance. The method was briefly the following. The 

 ova were lightly packed in wet wool contained in a tin-plate box per-^ 

 forated in its bottom to admit air, and covered with a wooden cover 

 that had been soaked in water, with the intent of preserving moisture. 

 The box was wrapped in tow, loosely covered with oiled paper, and 

 the whole, in an envelope of common writing-paper, was well secured 

 by a binding of thread. Thus prepared, the ova were sent by post 

 to Penzance, in Cornwall, a distance exceeding 500 miles, with tha 

 request that they should be sent back by return of post unopened. . 

 The first experiment was made on the 9th of November. The number 

 of ova sent was thirty, taken from the common stock without selec- 

 tion. They were received on their return on the 14th of the same 

 month. On taking them out, all were found transparent ; but, with 

 the exception of one, all became opaque on being put into watei^ 

 and that one, after a few days, also underwent the same change. : i' 



The second experiment was made on the 14th of November. Twenty 

 ova then sent were returned on the 18th. AH became opaque on 

 being put into water. jr/x« 



The third experiment was made on the 1st of December. Twenty 

 ova then sent were returned on the 5 th. Put into water, eleven 

 became opaque within a minute; most of these were slightly shrivelled. 

 After three hours, two more became opaque. After forty- eight hours, 

 four only remained transparent ; in these, under the microscope, the 

 circulation was found active in two ; in the other two it could not be 

 detected. One was hatched on the 31st of December, the other died 

 before hatching. 



The fourth experiment was made on the IStli of December. 

 Twenty-two ova then sent came back on the 17th. During the 

 interval there was a severe frost ; the thermometer here in the open 

 air was constantly below the freezing-point, and it would appear to 



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