632 
Diameter of stem 0,4 millimeters. 
Length of stem 0,4 
Length of vesicle 1,5 + 
Width of vesicle 1,0 ss 
Length of invagination 0,8 Pr 
Width „ N 0,5 i! 
Diameter of opening of invagination 0,03 2 
At first it was somewhat difficult for me to interpret the meaning 
of the specimen because there is a yet absolutely no mark of the 
embryonic body. The lo- 
cation of the allantois 
does, however, give us 
some clue to the future 
position of the embryo. 
It is somewhat compli- 
cated through the yolk 
cavity extending into the 
stem, but I do not think 
this is serious. I think that 
there is but one rational 
interpretation to the spe- 
cimen, i. e., it is an in- 
version of the membranes. 
The invagination is the 
cavity of the amnion. It 
is comparatively easy for 
us to imagine how this.em- 
bryo may be changed into 
one a little older, as for 
Fig. 1. Sagittal section of the embryo. Taken from the reconstruction. Enlarged 
33 times. 
instance Graf Sper’s. After the opening of the invagination, closes 
the walls « and a approach each other and the layer 6 and 6 move 
down on either side of the invagination. Then the neurenteric canal 
breaks through. This is practically the state of things as we find them 
in Graf SpErE’s embryo. 
It is quite as easy for us to imagine the formation of this 
bermyo from the single cell when we consider the excellent researches 
