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 posteiior 

 end of the Anlage of the Wolffian duct. As compared with fig. 

 26, the Wolffian duct Anlage in fig. 27 is now considerably 

 smaliei' 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 

 (ecL), 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 

 3'olk spheres ; their large and somewhat irregular nuclei are 

 generally situated on the outer sides of the cells next the 

 ectoderm. ( x 200. ) 



