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and occasion gill fever, or some think gill fever may cause 
shortening of the gill covers. 
On being hatched the appearances presented are peculiar. 
A large ovoid sae, the yelk sac, equal in length to about half 
that of the fish, passes from below the throat backwards and 
downwards, its posterior end sometimes being rounded, but in 
‘some instances ending in a sort of nipple-shaped point. Over 
its surface ramify numerous blood vessels, and the large umbilical 
vein conveys blood from it to the heart. Numerous oil cells are 
visible through its thin walls, also the liver and the vessels 
which supply it. Although the formation of the fins is fore- 
shadowed, distinct rays are not visible. The various blood 
vessels, the pulsation of the heart, and the appearance of 
contractions in the caudal sinus are very distinct. The entire 
length of these little fish averaged about half of an inch. 
On March 13th I found, different from what I had observed 
for the last few days, that the pectoral fins were no longer in 
constant motion, so I concluded that their necessity for thus 
assisting respiration had normally ceased. So I took one of 
these fish, now measuring 0°85 inch in length, and at 11.7 a.m. 
placed it in a tumbler of still water inside a room, the water as 
removed from the hatching tray being 42°. which rose in the 
room to 45° at 11.20. The fish had only been seven minutes 
when the pectoral began to be worked at the rate of three 
times to every movement of the gill covers, but as the little 
fish evidently became distressed, it was returned to the hatching 
tray, when its pectoral movements gradually ceased. 
Among the hatched fish I have only observed one mon- 
strosity, it having two heads, while after the hatching was 
completed only twelve bad eggs remained. 
March 20th, the little fish in the trays seem not altogether 
comfortable, a few having died, so I turned in a heap of fine 
sand in each, which appeared to give great satisfaction.* 
December 23rd, three of the eggs having been placed in 
a half cell containing water under the miscroscope, and in a 
* Up to May 26th, no further deaths occurred. The double headed one 
died May 25th. 
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