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305 
fluid they are in being now suitable for their existence? But 
another cause may have been the real one, viz., that the tem- 
perature had risen from 3° to 6° during the preceding twenty- 
four hours, and it is well known that warmth as much hastens 
hatching as cold retards it. A few still continued hatching 
daily, fifteen on the eighty-seventh day, five on the eighty- . 
eighth, two on the eighty-ninth, twenty-nine on the ninetieth, 
and fourteen on the ninety-first day. The eyes of the embryo 
were first very distinctly visible with a magnifying glass on 
the fiftieth day, but had been so for some time under the 
microscope. 
The appearances presented by young trout when just hatch- 
ing have been frequently described, consequently only call for 
a few remarks. Some embryos are stronger than others, and 
sometimes while looking at an egg it splits; first the head of 
the fish emerges, and a good plunge or two causes the shell 
to open along the back, or should the embryo not be very 
strong, it may be choked with its head emerging from the shell. 
Or one may be seen with its head entirely enveloped in the 
shell, but the rest of its body free, then with a dart it passes 
to another portion of the tray leaving the shell en route, at other 
times requiring more exertions for this purpose. In one case 
the yelk sac protruded first, and the young was a long time 
hatching. 
A number of young fish huddled together, as they commonly 
are in one corner of the hatching tray, occasion a constant 
current with their pectoral fins, which is clearly beneficial, not 
merely as preventing dirt attaching itself to their gills, but 
also in driving away their now vacated shells. Having closely 
watched these fish when hatched, I do not find the gills this 
year partly uncovered by the opercles, as I have often seen in 
former years.* Short gill covers may permit irritation of gills 
* Respecting young char Davy observes, “when first hatched the bran- 
chial arches are naked, that is, fully exposed to view, the gill-covers as yet 
not being sufficiently developed to hide them. As in the instance of Sal- 
monide and of other osseous fishes, no branchial filaments are known to 
exist in the foetus. May not this place be supplied by this naked state of the 
branchie ?”—Phil. Researches, p. 241. 
