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nounced than in the preceding stage. The 
Wolffian duct (W.d.) opens into the coelom 
above the pancreas. Above this opening, which 
in the reconstruction is covered by the mesothelial 
lining of the body cavity, are two small pro- 
nephric tubules (Proneph.). The mesonephric 
tubules (Mes.t.) are broadly connected with the 
coelom and, looping over the Wolffian duct, 
end in slight expansions. 
The atrium (At.) and ventricle of the heart 
are separated by a slight constriction. The 
pericardial cavity is cut off from the coelom at 
the median line by the septum transversum 
There are four complete aortic arches and 
the fifth is in the process of formation. The 
vena capitis medialis is now completely separated 
from the aorta. As in the preceding recon- 
struction, the vitelline artery (A.vit.) arises from 
two trunks, and behind the second root, the 
third pronephric artery forms a marked dilatation 
of the aorta. 
Figs. 13 and I4. Graphic reconstructions 
of an embryo 15 mm. in length. Normal 
plate series No. 26. (H.E.C. 227.) 
Fig. 13% 28, Big; 14% 33. 
In Fig. 13 a return is made to the general 
style of illustration employed in Fig. 10. However, 
no attempt has been made to represent by shading 
the moulding of the lateral surface of the pharynx 
and all the veins except the common cardinals 
and the proximal end of the vitelline have been 
omitted. 
The telencephalon (Telen.) is widely ex- 
panded, and the deep infundibular sack is 
curved a little cranially. The velum trans- 
versum and the paraphysis (Pa.) are well marked. 
Behind the paraphysis is the elongated epiphysis 
(Epi.) which is now distinctly divisable into an 
expanded distal portion and a narrower proxi- 
mal stalk. The mesencephalon is somewhat 
expanded and is sharply marked off from the 
hind-brain posteriorly by a distinct rhombo- 
mesencephalic fissure (F\r.-mes.). The hind-brain 
“ 
. 
