50 THE OVUM AND 



usually takes place around the nucleus in other cells; and again, 

 the germ-vesicle disappears, precisely as the nucleus of other 

 cells is generally absorbed. There is then no evidence that the 

 fluid of the germinal vesicle exercises a fructifying influence ; 

 but if it be the cell-nucleus, it disappears, because it has com- 

 pleted its office, — the formation of the yelk-cell. The disc, 

 which has formed around it, becomes developed into the 

 germinal membrane, and it is uncertain whether the remains 

 of the germ-vesicle also take part in that formation. 



We shall next proceed to the consideration of the other 

 contents which the yelk-cell includes in addition to the germ- 

 vesicle, making use of the bird's egg for the purpose. Setting 

 aside some points of distinction of slighter importance, the 

 globules, well known as present in the yelk of the hen's 

 egg when laid, may be divided into two principal classes : a, the 

 globules of the yelk-cavity ; and b, those of the true yelk-sub- 

 stance. The former (a) are not only present in the yelkrcavity, 

 but occur also in the canal leading from it to the germinal 

 membrane, and in the little prominence, called by Pander the 

 nucleus of the tread (Kern des Hahnentritts). When many 

 of them lie close together, they exhibit a white colour, whilst 

 the true yelk-globules in such circumstances appear yellow. 

 They may also be distinguished from the latter globules under 

 the microscope, (see pi. II, fig. 2.) They are perfectly round 

 globules, with quite smooth edges, each enclosing a smaller one, 

 which is also perfectly spherical, and looks like an oil-globule, 

 being rendered very distinct by its sharp outline. 



The remaining space in the large globules is usually trans- 

 parent, and not graimlous. But some may be observed which 

 have granulous contents, and they then completely resemble 

 the true yelk- globules, except that the latter do not gene- 

 rally contain any smaller ones with such dark outlines. Some- 

 times also, the globules of the yelk-cavity contain two or more 

 such smaller ones. The common yelk-globules (b), that is, 

 those of the true yelk-substance, may be distinguished from the 

 above-described by the following characteristics : they are upon 

 the whole larger, they have all granulous contents, and, for the 

 most part, do not enclose any smaller globules. They are very sen- 

 sitive to the action of water, which causes them to fall to pieces, 

 and then the granules enclosed within them becoming free, give 



