24 DHT AINE [VoL. XII. 
After the eggs are shelled they are rinsed in the hardening 
fluids and transferred to a large quantity of strong alcohol, say 
94%, which is changed frequently the first few days. If not 
treated in this way, the yolk is likely to swell and crack. _ Brit- 
tleness of the yolk is much diminished by the prolonged treat- 
ment with acids. 
The most beautiful surface views are obtained by staining 
the whole egg in borax carmine, or almost any haematoxylin, 
for a very short time, one-half to one or two minutes, and 
then washing in acid alcohol. This method gives very sharp 
and luminous surface contours. It has been used on a great 
variety of objects, arthropod and vertebrate embryos, etc., and 
is very useful. 
But this method cannot be used if there is any surface cuticle 
present. The whole egg must in that case be stained through- 
out, and the color subsequently drawn completely out of the 
yolk by acid alcohol (10 to 15 drops strong hydrochloric acid 
to 100 c.c. of 70% alcohol). The decolorizing process may 
require several days, and the acid alcohol must be changed as 
often as it is discolored. When this is successfully done, the 
yolk has the transparent, yellow color it had before staining, 
but the nuclei are bright red. 
If the eggs are to be mounted, after clearing in oil of cloves, 
they are split in halves with a delicate knife, made by grinding 
the end of a needle down to a very thin blade. 
The halves with the embryos on them are arranged like serial 
sections, in shallow cells, and fastened in position with a small 
drop of thick collodion and clove oil. The fixative is hardened 
by washing in turpentine, and finally the eggs are mounted in 
balsam. 
Each embryo was numbered, drawn, and in most cases finally 
taken out of the balsam and sectioned. 
The embryos were studied with raised condenser and wide 
open diaphragm, so that they appeared bright red on a clear 
yellow field. 
In such preparations the elevated surfaces and protruding 
organs appear dark, the depressions light. All the drawings 
have been outlined with the aid of a camera from such prepara- 
