TRANSACTIONS OF THE SECTIONS. 
597 
became developed : some were placed in a small glass lull of 
water, in a house situated on the banks of the river ; these not 
having been transported so far, and having consequently been 
less disturbed, underwent the natural change, and grew to the 
length of an inch. The period of development in such circum¬ 
stances varies with the temperature of the apartment, and may 
thus be produced ten days or a fortnight before their natural 
evolution in the river ; but exposure to the sun kills them in¬ 
fallibly. Having cast the slough, they will live about ten days 
in water unchanged, apparently thriving, growing, and darken¬ 
ing in colour, (if exposed to the light,) but they have not been 
observed to eat anything offered them, and they invariably die, 
whether the water be changed or not, after attaining the length 
of an inch and a quarter. The author has ascertained that the 
grown smelt has not an equal capability of living in unchanged 
water, but when confined in the same manner, quickly sickens 
and dies. 
On the 25th of March, it was found that nearly all the fish in 
the bed of gravel had cast the outer shell, and, from the appear¬ 
ances, it was concluded that this operation had taken place two 
days before ; and, therefore, that 142 days had elapsed from 
the time of the deposition of the ova, till the fish were disclosed. 
The author is disposed to believe that this period of twenty 
weeks may be subject to some variation, according to tempera¬ 
ture and other causes, but he rejects the idea, that ova deposited 
in the beginning of April, could become smelts in the begin¬ 
ning of June, since this would require the admission that eight 
weeks in the spring would produce the same effects as twenty in 
winter. 
Several of the young fry, now disclosed, were put immediately 
into a tumbler of water, and six were carried to Edinburgh ; 
and of these only one survived ; it lived five days in water twice 
changed, and died on a crumb of bread being thrown in, which 
troubled the clearness of the water; but all those which were 
kept in a house near the river lived, and were well on the 1st of 
April, in water which had not been changed. 
When first observed in the gravel bed, after bursting the 
shell, they were somewhat less than an inch in length, with the 
yolk of the ovum very large, and in the usual situation ; they 
appear to remain in this state under the gravel about eight days, 
and then emerge and haunt the edges of the river in shallow 
places. On the first of April, when the young fry emerged, 
the temperature of the gravel bed at 9 a. m. was found to be 41°, 
that of the water 43°; but by 12 o’clock the water was at 45°, 
and the air 55°, The author conjectures the temperature of 
