62 BULLETIN OF THE UNITED STATES FISH COMMISSION. 
toplasmic processes and separate cells occurring all round. The cause 
of this sudden change was doubtless the impurity of the water (for the 
proper apparatus had not yet been fitted up), the metallic pipe (block- 
tin) containing an opaque whitish deposit which speedily killed the 
ova. The addition of methylated spirit in the same way sends all the 
eggs and embryos to the bottom. Professor Sars, indeed, mentions 
that if the eggs of the cod are placed in fresh water they sink and 
never rise again, but are killed— just as a newly-hatched salmon is 
killed, though somewhat more slowly, by immersion in sea- water. He 
thinks that even a fall of rain might affect the floating ova in the sea, 
but this is unlikely. 
More than once the eggs of the haddock and other fishes have been 
brought under notice as bjdng on the bottom of a vessel, and therefore 
held as proving that the ova did not float; but in every case such eggs 
were found to be dead, dying, unripe, or unfertilized. If, in removing 
the eggs from a fish, too much pressure is applied, unripe eggs escape. 
Such either sink or float ambiguously, according to the stage of devel- 
opment. Unless this fact is borne in mind disappointment naturally I 
occurs, especially to one who has triumphantly carried such eggs from 1 
deep-sea fishing to vindicate statements that have been impugned, j 
No one ever asserted that dead eggs floated. It is the ripe and living 
eggs that are so buoyant. 
In the marine laboratory it has happened that some living ova of the 
cod rolled on the bottom of the vessel, but this was clearly due to the 
attachment of fine particles of mud and sand which had gained admis- 
sion from imperfections in the temporary apparatus, and which surely 
and speedily in every case proved fatal to the embryo. 
The ova and embryos brought from the surface of the sea are com- 
paratively hardy, even though kept for ten days without renewal of the 
sea-water. The lively little cod, about 5 mm . in length, with their char- 
acteristic black pigment-patches, swam actively at the surface of the 
water, darting hither and thither when interfered with, while a stratum 
of the dead lay at the bottom. The water may even be somewhat 
milky and the odor characteristic, and yet the embryos survive until, 
as Professor Sars also found, the yelk-sac, which supplies them with 
nourishment, is absorbed. 
The difference between the larval cod and the young salmon just 
hatched is striking. The former is in a very rudimentary condition, not 
only in size, but in structure. For instance, the heart pulsates, but as 
my colleague, Professor Pettigrew, observed, there is no visible blood 
and no blood-vessels. Those, therefore, who say that the heart in ani- 
mals contracts from the stimulus of its living blood, would here find 
little support. On the other hand, the newly-hatched salmon has at- 
tained considerable complexity of structure, and its blood-vessels are 
well elaborated. 
St. Andrew’s, Scotland, November 10, 1886. 
