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PROCEEDINGS OF SECTION D. 483 
In addition to the examination of living eggs, the following 
methods were followed :— 
1. The eggs were put in a ten per cent. solution of nitric acid 
and left in it for half an hour, then thoroughly washed in water, 
and passed through ascending grades of alcohol to 90 per cent. 
This was found to be by far the best method for most phases in 
the development ; the nitric acid readily passes through the egg- 
membrane and produces a strong whitening effect on the blasto- 
disc, leaving the yolk unaffected and translucent; the shrinkage 
is very slight. With this, as with the other methods employed, 
series of sections cannot well be made by the paraffin method, 
owing to the great brittleness of the yolk, especially in the earlier 
stages, and recourse must be had to celloidin. 
2. The eggs were fixed with Perenyi’s fluid, allowed to act for 
half-an-hour, and followed by ascending alcohols. This method 
preserves the eggs well, but is not so serviceable as the preceding, 
as it does not produce so great a whitening effect on the proto- 
plasm of the blastodise. 
3. The eggs were treated with osmic acid, followed by Merkel’s 
fluid, as used by Agassiz and Whitman in their studies on 
pelagic fish-eggs. This method is of very great value in differen- 
tiating the periblast and the periblast cells from the other 
elements. 
General Features of the Egg of Chilobranchus. 
The eggs are very small, being only 1-2mm. in long diameter. 
They are nearly always of oval shape (though a few spherical 
examples were found), and the short diameter is lmm. The egg 
is cemented down by one side; the blastodisc is sub-polar in 
position, but nearly always inclined towards the upper side of 
the egg (z.e., that side cemented to the surface of the stone) ; its 
position would therefore seem to be a polar one, slightly modified 
by the action of gravity. In a small percentage of cases, how- 
ever, the blastodisc was found to be situated in the middle of one 
side of the egg, which brought about marked changes in the 
general form in certain stages, as will be afterwards noticed. A 
few abnormalities were observed, of which the most interesting 
were two cases, in each of which there were ¢wo two-cell stages 
close together. It is very likely that these were not natural, but 
resulted from mechanical action during the removal of the eggs 
from the stone. There were a good many eggs, however, in 
which development seemed to have been arrested, there being 
only an abnormal blastodisc with a softened yolk. Such were 
probably eggs that had accidentally escaped impregnation. 
Circumstances were not favourable for investigating the history 
of the egg previous to the beginning of the process of segmenta- 
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