74 
ON A PLATYPUS EMBRYO. 
Anlage of the duct is very delicate, and, as in the preceding 
figure, has been broken in the process of section cutting. The 
tubule Anlage is rounded in shape, and consists of radiating cells 
surrounding a small lumen. It is now free from both the somite 
. and the lateral mesoderm. ( x 340.) 
Figs. 27, 28 and 29 represent three successive sections through the posterior 
end of the Anlage of the Wolffian duct. As compared with fig. 
26, the Wolffian duct Anlage in fig. 27 is now considerably 
smaller and thinner, and is connected at its outer edges with the 
ectoderm. In fig. 28 the Anlage is still more reduced in size, 
consisting of a single layer of cells, while in fig. 29 it is reduced 
to a single cell, connected at both ends with the ectoderm. 
Behind the section from which fig. 29 is drawn there is no longer 
any trace of the Wolffian duct Anlage. The Anlage of the 
tubule in fig. 27 appears as a rounded projection of the inter- 
mediate cell mass, with radially arranged cells, but in figs. 28 
and 29 this radial arrangement is lost, and the Anlage appears 
as a slight elevation of the mass. ( x 340. ) 
Fig. 30. — Transverse section through the wall of the blastodermic vesicle 
some distance beyond the amniotic area, showing the ectoderm 
(ect.), vitelline entoderm (vit. ent.) and mesoderm. The latter 
consists of a layer of cells below which occur numerous 
vasifactive cells [vas. c.) ( x 320.) 
Fig. 31. — Transverse section of the wall of blastodermic vesicle some 
distance further out than fig. 30. The mesoderm here consists 
of a single layer of spindle-shaped cells, while vasifactive cells 
have almost entirely disappeared. ( x 320.) 
Fig. 32. — Transverse section of wall of blastodermic vesicle at the ant- 
embryonic pole. Ectoderm and vitelline entoderm are alone 
present. ( x 200.) 
Fig. 33. — Vitelline entoderm cells of blastodermic vesicle drawn as seen 
through the ectoderm. They are filled up almost entirely by 
yolk spheres ; their large and somewhat irregular nuclei are 
generally situated on the outer sides of the cells next the 
ectoderm. ( x 200. ) 
