Sexual Characteristics of Oysters. 39 
knife with the free hand. When cutting sections it is neces- 
sary to keep the knife well wetted with alcohol, so that the 
sections may readily slide off on the upperside of the blade. 
Water should not be used to wet the knife, as it would get 
on the block of tissue, dissolve the gum, soften the surface 
to be cut, and injure the succeeding sections. ‘The sections 
are lifted from the knife as fast as cut, with a camel’s hair 
pencil, and\ chrown into a dish of water, in which the gum will 
dissolve out in a few minutes. The sections are then ready 
to be stained; and in order to clearly differentiate the herma- 
phroditic character of the reproductive glands of Ostrea edulis, 
a special staining reagent must be used. The one which 
gives the best results and acts most quickly will be given here. 
Equal parts of dense alcoholic solutions of safranin red and 
methyl green * are poured together and diluted with about 
eight times their combined volumes of water, producing a dark 
purplish solution of about the colour of claret wine. Into 
this the sections may be thrown and allowed to remain until 
completely saturated with colour, or until they are opaque: 
they may remain in the staining-fluid from one hour toa day ; 
but two or three hours is a sufficient length of time. When 
removed from the staining-fluid they are too deeply stained to 
be mounted at once, and must therefore be transterred to 95- 
per-cent. or absolute alcohol, and stirred about in it until the 
safranin red is no longer given off in clouds from the sections ; 
but it is important to note that if the sections remain in the 
strong alcohol too long the whole of the safranin will be washed 
out. In order to prevent this, when it is seen that the sec- 
tion has acquired a rosy red hue, combined with a bluish-green 
tint in the parts stained by the methyl green, the object should 
at once be removed from the alcohol, thrown into oil of 
cloves and mounted in balsam or damar. The extraction of the 
superfluous colour requires from five to fifteen minutes, accord- 
ing to the thickness and character of thesection, and should 
on no account be allowed to proceed too far; if it does, the 
peculiar and important staining-effect of the safranin is lost. 
As first poited out by Flemming, it has the peculiar property 
of stainmg the nucleus and its contents while it may be 
totally removed from other parts of the cell; in fact, as in 
the oyster-egg, it may be entirely removed from the nucleus 
and left only in a part of the nucleolus. The methyl green, 
on the other hand, does not tend to stain the eggs, but rather 
the spermatozoa and the cells from which they are derived ; 
and it is one of the most astounding facts known to histological 
* These are both aniline colours; the first is hard to obtain, except 
from dealers in dyers’ colours. 
