IS THE TKOPHOBLAST OF HYPOBLASTIO ORIGIN? 587 



certain points of agreement between its early development 

 and that of Pteropus, whilst Leche's anatomical work (' Kgl. 

 SvenskaVet.Akad.Handl./ Bd.xxi, 1886) upon Galeopithecus 

 points in the same direction. Of this genus I have now in my 

 possession several series of sections made through segmen- 

 tation phases, some of which I have here figured. 



These sections leave no doubt that the trophoblast of 

 Galeopithecus originates by delamination at as early an age 

 as the two- and four-cell segmentation stage, and render it 

 utterly futile to try and explain the Galeopithecus tropho- 

 blast as "due to an overtiow of the yolk or hypoblast cells 

 over the epiblastic i-udimeut" (Assheton, I.e., p. 228). 



If we look more closely at the three stages of Galeopi- 

 thecus here figured and begin with the one that is the furthest 

 developed (Text-fig. 1), we find full coincidence with a similar 

 stage described by Asshetou for the sheep (I.e., 1898, Pi. 16, 

 figs. 14, 15), by Keibel for the stag ('Arch. f. Anat. and 

 Phys. Anat. Abt.,' 1902, p. 292), by Weysse (' Proc. Amer. 

 Acad.,' vol. XXX, p. 28o) for the pig, by van Beneden for 

 the rabbit and bat ('Archives de Biologie,' vol. i), by 

 myself for the hedgehog, for the shrew ('Quai-t. Journ. 

 Micr. Sci./ vol. 80, PI. 17 : vol. 31, Pis. 36, 37), for Tupaja, 

 for Tarsius ('Verh. Akad. Wetensch. Amsterdam,' vol. iv, 

 1895, Pis. 1, 2; vol. viii, 1902, Pis. 1, 2), and for Nycti- 

 cebus (' Keibel's Normentafeln,' 1907), as well as by other 

 embryologists for various other mammals. This is the 

 common starting-point in which there is a trophoblast and 

 an embryonic knob with a cavity below it, and in which a 

 hypoblast is not as yet distinctly developed, although just 

 beginning to msike its first appearance. It should be borne 

 in mind that this very stage is thus characteristic for genera 

 of mammals so diverse as those mentioned above. The 

 way in which Asshetou attempts to prove from yet earlier 

 stages of the sheep that the outer trophoblastic layer is in 

 reality a derivate of the hypoblast sippenrs to me to be so 

 pre-eminently artificial (c.f. I.e. his figures 9-14) and the 

 argumentation so weak, that I must ascribe to a similar 



