18 CARL GOTTFRIED HARTMAN 



In one case the chromosomes of the polar body were arranged in 

 the equatorial plate of a division spindle. The position of the 

 polar body is, in the majority of cases, though by no means 

 invariably, at one pole of the elliptical egg, and the egg chromo- 

 somes lie in the cytoplasm just within the surface of the egg, 

 either exactly beneath the polar body, or, as is more often the 

 case, to one side of it. In a considerable proportion of the 

 eggs, the polar body is found at the equator of the egg, less 

 often at various levels between the pole and the equator, a 

 variation found to obtain also in ripe ovarian eggs. 



In a few of the eggs, particularly those of batch No. 56, one 

 very large fat vacuole (or black fat spherule if stained with 

 osmic acid) occurs at one pole of the egg, usually opposite the 

 polar body (fig. 4). Many eggs also show a peculiar body about 

 the size of a large fat spherule. It is homogeneous in structure 

 devoid of all granulation, takes a pink or lavender stain with 

 iron-haematoxylin and is surrounded by a light band, as if it 

 had shrunk away from the surrounding cytoplasm. Its position 

 in the different eggs is variable. Similar bodies have been 

 noticed in other mammalian eggs. 



Aside from the position of the polar body there is no evidence 

 of polarity in the tubal egg of the opossum, such as has been 

 described for ovarian and unsegmented uterine eggs of Dasyurus. 

 In only one case was there a preponderance of yolk granules at 

 one pole as compared with corresponding yolk-free granular 

 cytoplasm at the opposite or 'animal' pole. 



Insemination of the ovum no doubt takes place in the oviduct ; 

 for after the egg has received the albumen layer and the shell, 

 the latter forms an impenetrable barrier to the entrance of the 

 spermatozoa. Direct observations, however, of normal in semi- 

 nation in marsupials is lacking. In this connection Hill ('10) 

 says of the eggs of Dasyurus: '^ Apparently the ova are shed 

 almost simultaneously, and they must pass with considerable 

 rapidity down the tubes to the uteri where cleavage begins, for 

 I have only once found a tubal ovum, and that one had evidently 

 been retarded for some reason, and was polyspermic."'^ Selenka 



' Loc. cit., pp. 22-23. 



