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early stages, z.e. from the time of fecundation till the primitive 
cavity (furchungs hohle) is complete, are extremely difficult 
to make, and when made, still more difficult to float off on to 
the slide without breakage occurring. 
As soon as the primitive groove begins to make its appear- 
ance, the egg becomes tougher and comparatively easy to cut. 
I have found it better to place the ova, after they have been 
twenty-four hours in alcohol, in strong glycerine till they are 
thoroughly imbibed with it, and to imbed directly from this 
in the ordinary way. If care be taken to dry the outsides of 
the ova well on blotting-paper before putting them in the wax, 
they will be found to adhere very firmly to the imbedding 
substance. By the action of the glycerine after the spirit, the 
eggs become remarkably tough, and much easier to cut than 
when treated with spirit alone. A stock of prepared ova and 
embryos, and full grown tadpoles, may be kept in a bottle of 
strong glycerine, and cut at leisure. I have such a stock, 
which I have kept since last breeding season, and the ova 
now yield quite as good preparations as when just freshly 
hardened. I have not yet been able to try this method 
with the common fowl’s egg in very early stages, but expect 
it would yield excellent results. The section is treated in the 
same manner with absolute alcohol, whether glycerine be em- 
ployed or not. I find the best razors for the purpose, and 
indeed for all microscopic purposes, to be the flexible edged 
razors made by John Heifor, Sheffield, and stamped ‘‘ Made 
for the Army.” In order to render the edge flexible, these 
razors have their surfaces ground hollow. This hollow holds 
a great deal of spirit, and thus renders it easier to float sections 
off. Moreover, the edge is extremely thin, and thus does not 
act as a wedge on a brittle substance like a frog’s egg, and 
break the section in half. Again, these razors are extremely 
easy to sharpen, and every microscopist ought to be able to 
put a fine edge on his own razor. In cutting sections of ova 
in early stages, it will be found better to push the razor almost 
directly through, drawing it along very little, as in this stage 
the brittle substance resists compression much more firmly 
than extension. Of course, in later stages, and in cutting 
sections of ordinary tissue, it is better to use as much of the 
edge as possible, the razor here acting as a very fine saw. 
The sections should be allowed to remain about two minutes 
upon the slide ina drop of absolute alcohol. The slide should 
then be tilted so as to let as much as possible of the alcohol 
run off, and the remainder should be wiped away from round 
the section with a handkerchief, or soaked up with blotting- 
paper. A drop of oil of cloyes should now be applied to the 
