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ON A PLATYPUS EMBRYO, 
In its topographical relations the Wolffian duct in Platypus 
agrees with the conditions described by Meyer* in man, where 
according to him the proximal part of the duct leads back from 
the mesoderm while its distal portion is connected with the 
ectoderm. Both Meyer and Martin agree in describing the 
proximal part of the duct as mesodermal in origin, but as to this 
we are not in a position to speak with certainty. However, in 
Platypus the proximal part of the united Anlagen of the Wolffian 
duct and tubules is related essentially as Martin describes for the 
corresponding portion in the rabbit, and it might well be that as 
in that animal the proximal portion of the Wolffian duct Anlage 
arises from the intermediate cell mass in common with the 
Anlagen of the Wolffian tubules. 
Vascular System, 
Heart Anlagen : The symmetrically placed heart Anlagen have 
already been described in surface view as situated in greater part 
opposite the hind-brain region. Sections, however, show that 
their anterior ends extend somewhat beyond the posterior limits 
of the head plates of mesoblast, and we may therefore look upon 
these head plates as the regions in which the future aortic arches 
will be developed. 
The heart Anlagen at this stage in Platypus are essentially 
similar to those of a rabbit of about nine days. 
As the amnio-cardial vesicles are traced from their anterior 
ends backwards, they gradually increase in lateral extent, and at 
the same time towards the posterior limits of the head plates the 
thick splanchnic layer of mesoderm separates from the entoderm. 
In the space thus formed on each side, rounded vasifactive cells 
appear. Posteriorly these vasifactive cells have formed the 
vascular endothelium of the anterior cardiac region, and this lies 
in the gutter-like groove — open towards the entoderm — formed 
by the inbulging of the thick splanchnic mesoderm into the amnio- 
cardial coelom. Each heart Anlage consists anteriorly of several 
* Arch. f. Mikr. Anat. Bd. 36, 1890. 
