14 J. P. IIILL. 



excellence even as tlie fluids of Flemming and Hermann, 

 and thus iu sections usually all that represent it are a few 

 irregular cytoplasmic strands crossing a lai'ge, sharply defined 

 clear space (figs. 2 and 3, d.z.). The mass in question has 

 thus all the characters of the deutoplasmic zone of the full- 

 grown ovum, and it must undoubtedly be held to represent 

 the central portion of that which has not been utilised in the 

 upbuilding of the formative cytoplasm, and which has been 

 forced to take up an excentric position immediately below 

 the polar region of one hemisphere, owing to the increase of 

 the formative cytoplasm and its segregation in the other 

 hemisphere. 



The ripe ovum of Dasyurns thus possesses a polarity which 

 in its way is equally as striking as that of the Monotreme 

 egg. Towards the one pole the main mass of the ovum is 

 composed of dense, slightly vacuolated formative cytoplasm, 

 in which the polar spindle is situated peripherally, but nearer 

 the equator than the formative pole. Toward the opposite 

 pole and practically reaching the surface is a rounded mass 

 of greatly vacuolated deutoplasmic cytoplasm. Roughly, 

 the formative cytoplasm constitutes about two-thirds of the 

 bulk of the ripe egg, the deutoplasmic the remaining third. 

 Such being the structure of the ripe ovarian egg, if we 

 classify it at all, we must place it, it seems to me, with eggs 

 of the telolecithal type. My view of the significance of this 

 marked polar diiferentiation of the constituent materials of 

 the ripe ovum of Dasyurus I shall presently indicate. Mean- 

 time I would lay special emphasis on the fact that the 

 eccentric mass of deutoplasmic cytoplasm represents material, 

 surplus deutoplasmic material which has not been utilised in 

 the upbuilding of the formative cytoplasm. 



The fact of the occurrence in the Eutherian ovum of a 

 polar differentiation of its constituent materials is now 

 definitely established, thanks especially to the valuable 

 researches of Prof. 0. Van der Stricht and his pupils — H. 

 Lams and the late J. Doorme. In this connection I wish to 

 refer here in some detail to the extremely interesting obser- 



