114 BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The difference with regard to color begins now also to be noticed. 
The living roe is more or less of a yellowish-red color, whereas the dead 
is of a gray color, with a regular white spot on the under side of each 
egg. That the healthy color was lost with life was so natural that I 
passed it without any further investigation ; but my whole attention was 
directed to the examination of the above-mentioned white spot, which 
was invariably found in all dead eggs, when taken directly from the 
fish, as well as when they had been in the hatching apparatus any time. 
They all presented, under the microscope, a cloudy apppearance, as if 
a white membrane lay on the bottom of each egg. Later on, I became 
convinced that such was the case; for the white spot was simply the 
membrane bag which contains the yolk (vital fluid), and sinks to the 
bottom of the egg after being broken and its contents mixed with the 
white of the egg. 
It appeared as if outside violence to the fish was the cause of the 
eggs being thus destroyed (as, for example, pressure on the belly of the 
fish) ; and I began to feel so sure on that point that I came to the con- 
clusion that to handle the parent fish with care would be the surest 
way to prevent its occurence, when an incident came to my assistance 
and led my researches in another direction. Among the fish procured 
was a splendid pair of light-gray deep-sea cod, one a roe and the other 
a milt fish. All the roe from time to time obtained from these fishes 
was, to my great regret, useless, and at last I gave up all hope of getting 
any hatchable roe from them ; but as they were fine specimens and of 
a very large size, I decided to keep them in the hatchery basin, for the 
benefit of visitors and spectators. The water in which they were kept 
was often renewed with fresh sea- water, taken from a depth of 9 fath- 
oms. Some time afterwards I happened by chance to catch one of 
them, and to my surprise I got exclusively good roe from it, and in 
considerable quantities. 
Experiments were commenced with a greater number of fish which 
had given more or less bad roe, and when the result in all cases was 
the same it was considered clear proof that the saltness of the water 
must be taken largely into consideration. It may be remarked that 
the water pumped into the hatchery from a depth of 9 fathoms con- 
tains twice the quantity of salt as that on the surface. 
It still remained to be explained why some fishes gave only useless 
roe, while all of them lived under exactly the same conditions and in the 
same place. I noticed that, as a rule, small-sized fish, of a dark color, 
gave the best roe for hatching, and, on the contrary, the light ones gave 
bad. Now the fish of light color live outside the coast in deep water ; 
and the darker live closer to the shore, and are commonly called fiord 
fish, bay or shore fish. I was convinced that it was not the greater or 
less amount of salt the water contained that made the difference, but 
the sudden change from the deep-sea to the fresher water on the sur- 
face. This was also further proved by some deep-sea cod that were 
