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Part III. — Ninth Anmtal Report 
2 occupies about 50° of the surface of the sphere. The cells are more or 
less polyhedral, especially in the centre of the blastoderm, and more 
rounded towards the periphery, the cells of the margin in places projecting 
on to the adjoining yolk mass. The blastoderm shows small oil-globules 
underneath and between the cells. 
On the second day segmentation made great advances and the blasto- 
derm increased till it covered 70° of the surface of the sphere. Fig. 3 shows 
the blastoderm towards the end of the second day, with the number of cells 
enormously increased, their size reduced, and their shape more rounded ; 
the intercellular ispaces are still numerous though small. The blastoderm 
maintains its slow growth and the embryonic rim {b.r.) is soon indicated, 
and becomes distinct six to twelve hours after the st-age shown in fig. 3. 
The embryonic rim broadens with the marked increase of growth of the 
blastoderm, and in fig. 4 the first indication of the future embryo (em.) 
projecting inwards from the embryonic rim is seen. The central part of 
the blastoderm is clear, due, as will be seen, to the thinning of this part of 
the blastoderm and to the sub-blastodermic cavity, while the thickened 
periphery makes the margin darker. In fig. 5 the further growth of the 
embryo is exhibited and the peripheral part, opposite the embryo, is pro- 
jected slightly and is stained deeper than the central part. The embryo 
continues to grow inwards and the blastoderm increasingly surrounds the 
yolk-mass. The embryonic ingrowth twelve hours after the stage figured 
5, showed an incipient division into head and body and the cells alongside 
of the embryo exhibit numerous oil-globules, but not till some hours sub- 
sequently is the division of the embryo into head and body clearly shown. 
In fig. 6, not only is this division into two parts shown but the head 
part shows the future forebrain (f.h.) and the optic lobes (op.). The fore- 
brain is a rounded prominence in front of the somewhat elongated optic 
lobes. The brain contrasts both as regards length and breadth with the 
narrow body or trunk portion. The nervous system (ne.) and the notochord 
(nc.) are continued from the brain-mass towards the caudal end, and occupy 
almost the whole length of the trunk of the embryo. Fig. 7 is a drawing 
of the embryo five hours older than that of fig. 6. The embryo is one 
half longer than that of fig. 6, and the breadth has increased in proportion. 
The divisions of the brain have become more marked, and the optic 
portions, while they have decreased in size, show a gradual separation from 
the central brain-mass. The region of the mid-brain (in.b.) is distinguish- 
able from the hind brain (h.b.) which has attained a greater breadth than 
the mid brain. An indication of the future brain capsule is shown at this 
stage, being more distinct in the region of the hind brain. The notochord 
(nc.) is seen through the nervous chord (ne.) into which is gradually merged 
anteriorly the hind brain (h.b.) 
The posterior end of the embryo in figs. 6 and 7 projects as a tail- 
swelling (t.s.) into the wide blastopore (bl.). 
Blastopore. — The successive stages of the formation of the blastopore 
(bl.) are easy to trace. After the formation of the embryo, the blastodermic 
rim becomes continually extended by the epibolic growth of the blasto- 
dermic area over the yolk-mass. In fig. 6 the blastopore occupies at least 
half of the peripheral surface of the egg, the margin of the blastopore 
being the outer part of the embryonic rim. With the growth and ex- 
tension of the embryo along the surface of the egg, the growth of the 
epibolic covering continues, reducing the size of the blastopore, the anterior 
margin of which is seen in fig. 7. One day afterwards the blastopore 
has decreased much in size till it assumes the elongated and somewhat 
rectangular appearance in fig. 8. Coincident with this lessening of the 
blastopore Kupfi'er's vesicle (k.v.) appears slightly in front of it. In fig. 8 
