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TEXT-BOOK OF PHYSIOLOGY 



while many are visible to the unaided eye, others require for their detection 

 high powers of the microscope. Although the follicles are present in the 

 ovary at the time of birth, it is not until the period of puberty that they as- 

 sume functional activity. 



From this time on to the catamenial period there is a constant growth 

 and development of these follicles. Each follicle consists of an external 

 investment of fibrous tissue and blood-vessels, and an internal investment of 

 cells, the membrana granulosa. At the lower portion of this membrane there 

 is an accumulation of cells, the proligerous disc (Fig. 323). The cavity of 

 the follicle contains a slightly yellowish, alkaline, albuminous fluid, a 

 transudate in all probability from the blood-vessels. The Graafian follicle 

 is of especial interest, for it is in this structure, and more especially in the 

 proligerous disc, that the true germ-cell or ovum is developed. 



FIG. 324. OVUM OF A Cow. i. *Zona 

 pellucida. 2. Cytoplasm, vitellus. 3. Nu- 

 cleus, germinal vesicle. 4. Nucleolus, germ- FIG. 325. FRONTAL SEC- 

 inal spot. 5. Corona radiata. The radial TION OF THE UTERUS, i. Cav- 

 striation of the zona pellucida cannot be it y o f the body. 2, 3. Lateral 

 seen. (StShr.) walls> ^ ^ Cornua. 5. Os 



internum. 6. Cavity of the 

 cervix. 7. Arbor vitae of the 

 cervix. 8, Os externum. 9. 

 Vagina. (Sappey. ) 



The ovum is a spheric body measuring about 0.3 mm. in diameter. It 

 consists of a mass of living, protoplasmic material, cytoplasm, a nucleus or 

 germinal vesicle, and a nucleolus or germinal spot. The cytoplasm presents 

 toward its central portion a quantity of granular material, partly fatty in 

 character, the deutoplasm or vitellus. The peripheral portion of the cyto- 

 plasm is surrounded by a clear thick membrane, the zona pellucida, external 

 to which is a layer of radially placed columnar epithelium, the corona radiata 

 (Fig- 324)- 



The nucleus consists of a nuclear membrane enclosing contents. The 

 latter consist of an amorphous material in which is embedded a network, 

 some of the threads of which have a strong affinity for certain staining 

 materials, and hence are known as chromatin, in the meshes of which lies a 

 material that stains less deeply and known as achromatin. 



