400 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to the meaning of the structures observed in the germinal vesicles of 

 various animals, and the relation of this ovarian nucleus to the 

 nuclei of ordinary cells. 



It is found that acidulated methyl green stains the chromatin or 

 network of the germinal vesicle, but leaves uncoloured certain struc- 

 tures within it. The nuclei of male cells are rich in chromatin, 

 which is stained by methyl green ; and they have no nucleolus, or 

 only a very small one. On the other hand, the nucleus of the 

 female cell has one or several large nucleoli, and is poor in chro- 

 matin. From this v. Wielowiejski confirms, by micro-chemical tests, 

 the homology between the polar bodies of the egg-cell, and the 

 cast-off remnants of division of the sperm-mother cell. M. van 

 Bambeke studied the germinal vesicle in a large number of Arach- 

 nids, Isopods, and insects, and confirms to a certain extent the results 

 of previous observers. He describes the varieties of the germinal 

 vesicle in different Arachnids ; and concludes that this structure is 

 a nucleus, the characters of which differ notably from those of 

 Ordinary nuclei. 



The objects were prepared by the following methods, either 

 stained with methyl green direct, or after certain fixing reagents : — 

 (1) osmic acid, 1 per cent. ; (2) glacial acetic acid ; (3) Fleming's 

 mixture ^ ; (4) mixture of 3 • 5 grm. chromic acid ; 14 grm. acetic 

 acid in 700 gr. water. The author considers methyl green the 

 staining agent, par excellence, for chromatin, though it is not an 

 absolute test for its presence. 



Development of the Mole.* — Mr. W. Heape finds that the ripe 

 ovarian ovum of the mole is surrounded by a thick zona radiata, 

 pierced by fine canals, and a very delicate vitelline membrane ; nothing 

 comparable to a micropyle in the zona, nor any follicular cells 

 within it were observed. The yolk consists of homogeneous vesicular 

 bodies, and of minute highly refractile granules, contained within 

 the meshes of a protoplasmic reticulum. The nucleus is rounded or 

 oval, and contains a single central nucleolus, together with a vary- 

 ing number of smaller or larger granules. Beneden's description of 

 the ejection of the vesicle to form the polar bodies and the subse- 

 quent non-nucleated condition of the ovum appears to be erroneous. 

 Segmentation commences with the appearance of two and then of four 

 segments, and is afterwards irregular ; the segments themselves are 

 of irregular size, and do not appear to be divisible into two kinds 

 (epiblastic and hypoblasts) as Beneden supposes. After entering the 

 uterus the segments divide into an outer hyaline layer, and an inner 

 deeply granular mass. Mr. Heape suggests that the vitelline matter 

 which was originally contained in all the segments alike, has passed to 

 the inner ones, so as to allow of the outer multiplying more rapidly 

 and flattening out to form the wall of the blastodermic vesicle. The 

 epiblast of the vesicular embryo is derived from the whole of the 

 outer layer, and by far the greater part of the inner mass of segments, 

 the rest of which forms the hypoblast; the mesoblast arises from 

 both primitive layers. 



* Quart. Journ. Micr. Sci., xxvi. (1886) pp. 157-74 (1 pi.). 



