( 495 ) 
tion of the other (figure 1c. and d.). The upper part of the phallus 
frame stands like a crest upon the cornerplace of the deviating 
lamellae. (fig. 1 b-d.). 
If we look more closely at the wall of the fossa navicularis, it 
appears that it is only partially formed by the lamellae of the 
phallus-frame; the rest originates from the penisectoderm, which by 
the side of the phallus-frame bends like a fold over its edge (marked 
in fig. 1 b and ec. with g.p.). If this fold is to be called sexual- 
fold, it must be borne in mind that it does not represent the tran- 
sition-edge of the phallus-frame into the penisectoderm, but entirely 
originates from this ectoderm. In figure 1 b the two sexual folds 
are situated close to each other, in figure 1 ¢, corresponding to the 
middle of the fossa navicularis they are farther distant. 
Towards the base of the penis the two lamellae of the phallus- 
frame remain each other’s continuation; likewise the median crest 
remains present; the two sexual folds, on the other hand, keep 
bending to one another till they reach each other in the median 
line and close the urogenital canal. Accordingly the wall of this canal 
consists of two parts, originating from the phallus-frame and from 
the sexual folds (penisectoderm) (fig. 1 d.). At the nature of the 
epithelium they are to be recognized microscopically. 
In the discussion of the older embryos I shall restrict myself to 
that place, where comes about the closure of the urogenital canal. 
I mention in passing that the part already closed, grows in length 
during the following time of development and contributes to the 
growth of the perinaeum. 
In an embryo of 5 em. the place where the two sexual folds 
meet in the median line, is situated somewhat behind the broadest 
part of the fossa navicularis. Here, too, the two wall-parts of 
the urogenital canal, originating from the phallus-frame and from 
the sexual folds are clearly to be distinguished from each other. 
The part of the phallus-frame not separated lies like a crest on the 
ventral wall of the urogenital canal; before the fossa navicularis the 
phallus-frame forms an epithelial double-lamella. In this embryo a 
praeputium has appeared which has not yet entirely grown about the 
penis. The closure of the urogenital canal now goes on in apical 
direction, so that the orificum externum urethrae is removed to the 
point of the penis. This removal runs almost parallel to the growing 
of the praeputium round the glans penis. 
In the closed part of the urogenital canal the wall every time 
consists of the two parts described higher up, which are microscopi- 
cally sharply to be distinguished. Differences appear only in the 
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