840 The American Natm-alist. [September, 
The entire yolk with the blastoderm should be left for half an hour 
in the glass with the nitric acid ; it may then, part of the acid having 
been poured off, be returned into a large dish full of water, which has 
to be changed several times. After the yolk has been for a few min- 
utes in the water the blastoderm has to be cut out with scissors, when 
it will readily peel off from the underlying yolk, and the vitelline 
membrane readily comes away. The blastoderm is then to be left for 
half an hour in water, which should be renewed, and then transferred 
to weak alcohol (60 per cent.), in which it should remain for twelve 
hours ; it should then be placed for two days in 90 per cent, alcohol, 
and then stained by immersion for three or four hours in Ehrlich's 
hjernatoxylin (crystallized haematoxylin 2 grnis., water 100 c.c, gly- 
cerine 100 c.c, acetic acid 10 c.c), followed for a few minutes by 
acidulated alcohol (97 c.c. 70 per cent, alcohol, 3 c.c. hydrochloric 
acid), and that in turn for half an hour or more by alcohol diluted to 
70 per cent, by the addition of ordinary tap-water or water artificially 
rendered slightly alkaline. The specimen will then be ready, after 
passing through 90 per cent, and absolute alcohol, for mounting as a 
whole. For sections it is better to omit the acidulated alcohol, and to 
allow the specimen three days further hardening in 90 per cent, and 
absolute alcohol. 
The important point here is, of course, the ease and rapidity with 
which the white is got rid of, so that a large number of blastoderms 
may be prepared in a comparatively short time. But the mode of sub- 
sequent treatment described above, which is applicable to blastoderms 
prepared in other ways, gives results, particularly for whole blasto- 
derms, such as are not obtained by any other of the many methods 
tried. 
