DEVELOPMENT AND GROWTH OF SALMON FRY. 



555 



previously taken place, when the pond had not been sufficiently imbedded with 

 gravel. 



To shew the effects of increased temperature in hastening the development 

 of the infant fish, I may relate an experiment which I made upon a few of the 

 same ova, from which this famUy proceeded. On the 20th of April (106 days 

 after impregnation), finding the ova alluded to unhatched, and the temperatm-e 

 of the stream being 41°, I took four of them and placed them in a tumbler of 

 water, covering the bottom with fine gravel, in which I imbedded the ova. I then 

 suspended the tumbler from the top of my bed-room window, above which I 

 placed a large earthenware jai-, with a small spiggot inserted in its side, from 

 which I easily directed a stream of pure spring water into the tumbler. The waste 

 water was carried out at the window along a wooden channel fitted up for the 

 pm-pose. As there was no fire in the bed-room, and the window facing the north, 

 the temperature did not range very high, 47° being the average, while the average 

 temperature of the water in the tumbler was 45°. During the night, however, 

 the temperature would be very considerably increased, and the consequence was, 

 the young fish in the tumbler were hatched in thirty-six hours, while those re- 

 maining in the stream did not hatch till the 28th of April, a difference of nearly 

 seven days. At this stage the Uttle fish are so very transparent, that their vital 

 organs are distinctly visible, and, when placed immediately under the eye of the 

 observer, they present a very interesting appearance. The pectoral fin is continu- 

 ally in rapid motion, even when the fish itself is otherwise in a state of perfect 

 repose. They also begin to manifest an increasing desire to escape observation, 

 a principle wisely implanted for their better security, during so feeble and help- 

 less a condition. On the 24th of May (thirty-nine days after theh birth), the fish 

 ii^.the tumbler were completely divested of the yolk, and the characteristic bars 

 of the parr had become visible. At this time they measured nearly one inch in 

 length, and appeared to be in perfect health ; but fearing that after the yolk 

 was consumed, I should be unable to supply them with appropriate food, I re- 

 turned them to the pond from which I had taken them on the 20th of April, where 

 they perished with the rest of the family. 



This last experiment proves, that by placing the ova under a temporary stream 

 of water in the house, the development of the young may be materially accelerated, 

 while it also shews that they may be kept alive for a considerable time after- 

 wards ; at aU events, until the yolk, which I presume to be their sole support at 

 this period, is totally consumed. 



The next experiment, the circumstances of which I have to relate, has been 

 attended with more success than those which I had previously made. The pro- 

 cess of taking the adult fish, and aU the circumstances attending the impregna. 

 tion, were entirely similar in this case to that already narrated. 



VOL. XrV. PART II. 5 E 



