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observed just at that point where a fissure is about to com- 
mence. A shallow depression is seen to form slowly, the dark 
substance of the ovum being apparently drawn inwards at one 
spot. The bottom of the depression is then slowly pushed 
forwards again, and the depression thus obliterated. These 
undulations continue for some time, the depression becoming 
deeper on each occasion, its sides becoming more and more 
vertical, till at length the return of the wave ceases, and 
the shallow cleft becomes permanent. The cleft rapidly 
deepens, and if it be now viewed directly from above 
a series of beautiful plications will be observed to form them- 
selves at right angles to it on its sloping sides. ‘The process 
of segmentation goes on until the ovum, from being first coarsely 
and then finely tuberculated, becomes smooth again. If, when 
this latter stage is reached, an ovum be broken with needles, 
and a portion of the contents placed on a slide covered with 
thin glass, surrounded with oil to prevent evaporation, and 
viewed with a quarter objective, it will be seen to consist of 
large rounded pigmented cells, having a transparent nucleus. 
These cells exhibit a curious movement. They throw out 
from their periphery one or more hyaline bladder-like pro- 
cesses. These processes are never drawn out into long threads, 
but remain nearly circular in outline. They are soon with- 
drawn, and fresh processes are thrown out. So far for the 
appearances which may be observed in the ovum in the fresh 
state. Now, as to the more difficult question of the investiga- 
tion of the relation to one another of the cells composing its 
internal structure. 
At each period of successive development, e. g. immediately 
on extrusion, then, when the first cleft is perfect, and then 
soon after the completion of the second, samples of ova should 
be taken and placed in a half per cent. solution of chromic acid 
to harden them for further examination. It is not necessary 
to remove the investing albumen. It disappears in the chromic 
acid. It is better to have a series of two ounce bottles with 
wide necks, and to keep the successive batches of ova apart. 
The ova will have a great part of their colouring matter dis- 
charged by the chromic acid solution, which will become much 
darker in consequence. As soon as this process is complete, 
and the ova look whitish, in about three or four days the 
chromic acid solution should be poured off, and alcohol 
(strength about 35 per cent.) substituted. After they have 
remained in alcohol about twenty-four hours, they are ready 
for imbedding and cutting. For imbedding, a small tray of 
blotting-paper should be made, about 14 inches long, 1 inch 
broad, and + an inch deep. A mixture of half part wax 
