IN RELATION TO THE DISTRIBUTION OF SPECIES. 
93 
Returned to water, its circulation was distinct at the end of forty-eight hours. Nine 
days after it was in a dying state. 
2. An ovum on a slip of glass was exposed to the air of a room at 52° for two hours. 
The shell then had become at one spot indented as from shrinking, the effect of eva- 
poration, yet the circulation seemed unimpaired ; but transferred to water, the circu- 
lation presently stopped, the egg becoming opake from the absorption of water, and 
of course dead. 
3. An ovum exposed to the air of a room on a watch-glass from noon till 4 p.m., 
the thermometer rising from 49° to 51°, had become dry and shriveled. From the 
state of the shell the blood-vessels were indistinct under the microscope. Put into 
water, in one or two minutes a rupture of the shell took place and the young fish 
escaped. It was very languid, only the slightest indications of life being perceptible ; 
yet the heart did not cease its feeble action till the eighth day, counting from the 
rupture of the shell. 
4. An ovum on a support of glass was exposed to the air of a room at 49° for an 
hour and ten minutes ; its shell was slightly indented. Returned to water, on the 
second day the young fish burst its shell, was vigorous, and so continued. 
5. An ovum was exposed to the air of a room during the night for about ten hours, 
the thermometer under 50°. The following morning it was found shriveled; put 
into water, the shell presently burst ; the young fish, excepting for a slight motion 
of its pectoral fins, appeared lifeless, and it soon died. 
6. An ovum placed on a rock in the open air in the shade at 38°, after two hours 
was slightly shriveled and its circulation had become languid. The following morn- 
ing its circulation had ceased, and it shortly became opake. 
7. An ovum placed on snow during a thaw with occasional gentle rain, the air 
about 34°, and kept there from half-past nine in the morning till four in the after- 
noon, did not appear to be shrunk, nor was its circulation interrupted. Replaced in 
water, its circulation the following day was active. 
II. Of Exposure to Moist Air. 
To ascertain the effect of exposure to moist air, I have made many experiments, as 
by placing the wet ova in watch-glasses covered with other glasses of the same size ; 
keeping them in moist wool, from which water had been wrung out ; and in vials 
slightly wet within ; in each instance taking the precaution to allow of the admis- 
sion of air. The trials have been made at temperatures varying from 34° to 50°. 
The results have been so uniform that I do not think it necessary to enter into mi- 
nute details. The ova in no instance appear to have materially suffered, whether the 
exposure has been for an hour or for several days. Thus, in one experiment, nine ova 
were kept in a vial, one of six-ounce capacity, eleven days ; examined then under the 
microscope, the circulation in each of them appeared to be vigorous, as vigorous as 
before ; and, replaced in water, they all produced healthy fish, and sooner on an 
