THE OVUM. 239 



mucin) in the secretion of the follicle. After having 

 been stained the sections are passed through alcohol 

 and oil of cloves, and mounted in dammar. 



Preparation 9. The ovum. The ripe mam- 

 malian ovum, although it can be seen within the 

 larger Graafian follicles in the sections of the 

 hardened organ, forms a much more beautiful ob- 

 ject when obtained isolated from the ovary of a 

 recently-killed animal. A full-grown doe rabbit, 

 not pregnant, is to be sacrificed for this purpose. 

 One of the ovaries having been removed, it is held 

 firmly between the finger and thumb over a clean 

 glass slide, in such a position that the largest and 

 most prominent Graafian follicle is almost in con- 

 tact with the middle of the slide. The follicle is 

 then picked with a sharp-pointed scalpel, so as to 

 cause the fluid contents of the follicle to spirt out, 

 carrying with them the ovum, surrounded by a 

 number of the epithelium cells. The ovum is rather 

 too small to be detected with the naked eye, but its 

 presence may be suspected if, on glancing at the 

 slide in such a manner that the light is reflected 

 from the surface of the fluid to the eye, a slight pro- 

 minence is observed on the otherwise flat surface. 

 Its presence here is confirmed by examination with 

 a low power, and it may then be carefully observed 

 with the ordinary high power. It is better, if pos- 

 sible, not to apply a cover-glass, for the zona pellu- 

 cida is apt to become broken ; and, moreover, even 

 slight pressure spoils in great measure the natural 

 appearance of the object But if the objective 

 becomes dimmed by its proximity to 'the fluid, or if 

 it is desired to employ an immersion, then a thin 

 cover-glass must be used, and to protect the ovum 

 from pressure a narrow slip of thick paper (an ordi- 

 nary hair is not thick enough) is to be put on either 

 side before the cover-glass is applied. If the fluid 

 which accompanies the ovurn from the Graafian 

 follicles is not in sufficient quantity, a drop of aque- 



