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formed by the ectodermic and eiitodermic vesicles, where the edge of 

 the latter turns out to become united to the trophoblast. These 

 pouches are situated on the right and left sides of the vesicle, that 

 is, they are in the same plane as that of the broad ligament of the 

 uterus, and consequently lie directly opposite to the right and left 

 openings of the fallopian tubes. The pouches rapidly increase in size 

 until the entire space lying between the ectodermic vesicle and the 

 Träger is filled up by them. Eventually the double-walled partition 

 separating the cavities of the expanded pouches breaks down, thus 

 producing a single large extraembryonic body cavity. 



The embryonic rudiments arise from the ectodermic vesicle, and 

 at first make their appearance as two blunt processes involving the 



EN.- 



4 



Fig. 4. Photograph of a median section of a vesicle which shows the be- 

 ginning of the mesoderm as two pouches (ilf). The free trophoblast (TE) will soon 

 slough off, thus exposing the entoderm {E^) to the cavity of the uterus. The 

 Träger (TA) is the thickened or placental portion of the trophoblast. 



right and left sides of the vesicle, that is, each process lies directly 

 above a mesodermic pouch. We shall designate these two outgrowths 

 as the jirimary buds. The apj)roach of the buds is anticipated, even 

 before they become visible as outgrowths, by the shifting of cells 

 from the roof to the sides of the vesicle, and by the time the buds 

 become established, their walls are considerably thicker than the roof 

 of the ectodermic vesicle (Fig. 5). 



Each primary bud soon bifurcates, giving rise to two secondary 

 buds, each of which forms the rudiment of an embrvo. In this 



