22 
DR. DAVY ON THE OVA OF THE SALMON, 
good progress of development, the eyes of the embryos being visible, and the blood- 
corpuscles distinct in the vessels of the vitelline membrane, when placed under the 
microscope, using a glass of one-inch focal distance. Without loss of time they were 
variously distributed ; some in shallow earthenware pans, some in finger-glasses used 
at table, and with water in all little more than sufficed to cover them. No gravel 
was added. The water employed was well-water of considerable purity, of about 50° 
Fahr., and was changed once daily, and once only. The vessels were kept in a room, 
the temperature of which seldom exceeded 50°, and was rarely below 46°. Most of 
these eggs proved productive, and have yielded young and vigorous fish. The first 
which broke their shell appeared on the 15th of February, the last on the 17th of 
March: of the total number not more than three or four aborted. 
The ova from the Dee were received on the 7th of February, conveyed by rail, and 
had been sent off the preceding day. One portion of them was in a two-ounce vial, 
two-thirds full of water ; another, in a vial of the same size full of water ; a third, in 
dry sand ; a fourth, in wet sand ; a fifth, in wet cotton-wadding ; and a sixth, in dry 
wadding : all enclosed in a covered box. These ova on arrival exhibited no signs of 
organic development. They were distributed immediately much in the same manner 
as the preceding, and were treated in the same way, but with a different result. All 
of them in succession became opake from imbibing water, and not in a single instance 
were there any indications afforded of vital progress ; leading to the inference that 
they were dead when they reached me. From Mr. Ayrton I have recently been in- 
formed that the ova remaining in the box from which those had been taken were 
doing well ; and hence, necessarily, the conclusion, that the journey had been fatal 
to those I received. This may have been owing to their having been sent at so early 
a stage ; and I may mention in confirmation, that a second supply which was for- 
warded to me later — three weeks later — sent by post in moist wool, in a more advanced 
stage, nearly as much advanced as those from the Leven, arrived alive and are now 
hatched. It may perhaps be said, that the treatment of the unsuccessful ova after I 
received them, especially as to the manner in which the water was supplied, was the 
cause of their failure : but this does not appear to me probable, having found it to 
succeed with the ova of the delicate Charr, — ova taken by myself from the parent-fish, 
and impregnated forthwith and immediately distributed in the same kind of vessels 
as those now used, and the water in which, of the same quality, was changed once 
only daily. 
Having premised thus much, I shall now describe the several experiments which I 
have made for the purpose of testing the power of endurance of the ova. Unless 
otherwise specified, it is to be understood that the ova in each instance used were of 
those from the Leven. v 
I. Of Exposure to the Atmosphere. 
1. An ovum exposed for an hour on a slip of glass to the air of a room at 64°, 
placed near a fire, became dry superficially without its circulation being stopped. 
