IN RELATION TO THE DISTRIBUTION OF SPECIES. 
25 
glass by ice, and the inside of the glass was coated with ice, the greater portion of 
the egg however remaining in water. The ice thawed, the circulation was seen 
going on, and it soon became active. Twelve days after, the young fish burst its 
shell, was, and has continued vigorous. 
8. An ovum was exposed in water to the open air at 28°. In about two hours the 
water was frozen at the surface and spicula of ice had formed round the ovum, as it 
were shooting from it. Thawed on the following day, the circulation was found to 
be vigorous, and in eleven days a young active fish was produced. 
9. An ovum, one of those last received from the Dee, was exposed to the open air, 
placed on green moss, and left so exposed during three entire days and nights. It 
was then returned to water. In six hours after it was hatched. The young fish was 
languid and in point of size comparatively diminutive, as if prematurely produced, 
yet the action of the heart was vigorous, and the circulation as seen under the micro- 
scope normal. It may be right to notice the kind of weather that prevailed during 
the exposure of the ovum. During the first twenty-four hours the thermometer by 
day was between 36° and 38° ; there was some rain, '39 inch was the quantity, and 
partial sunshine ; during the night the thermometer on the grass fell so low as 29°'5 ; 
there was a little rain, *02 inch. During the second twenty-four hours the thermo- 
meter by day varied from 39° to 33°; the air most of the time was misty, but without 
rain ; at night the thermometer fell to 28°, yet, as there was no frost in the morning, 
it was probably so low only for a very short time. During the last twenty-four 
hours, the state of atmosphere and the temperature differed but little from what they 
were in the preceding. Part of the time, especially during the latter third, the ovum 
was a good deal protected by the leaves of the moss, between which it had sunk. At 
the end of the three days it was neither dry nor shriveled, and only very slightly 
indented, and that on the point on which it rested. It is worthy of remark, that it 
was the first hatched of the ova last received from the Dee ; and that the young fish, 
now six days old, is alive and thriving. 
IV. Of Exposure in IVater to a Temperature of, or above 70°. 
In these trials ova were employed and young fish, and chiefly the latter, as better 
adapted to show the effect of the high temperature. In each instance the ovum or 
young fish was put into a thin glass vessel of the capacity of about four ounce mea- 
sures, nearly full of water, and this vessel was placed in a water-bath of the tempe- 
rature required. The temperature given in each following instance was that of the 
water in which the subject of the experiment was immersed. 
1. An ovum kept two hours and a half in water at 70°, placed under the micro- 
scope, was found to have its circulation somewhat impaired, rendered more languid ; 
kept in two hours more, the temperature rising to 80°, no further injurious effect 
was produced, at least that was apparent. The vessel was now withdrawn from 
MDCCCLVI. 
£ 
