778 GENERATION. 



The ovum is globular, with a diameter of about -^ of an inch (165 to 

 170/x,) measured from the outer border of the zona pellucida. 



The zona pellucida (zona radiata, or vitelline membrane) is -^^ to -j-^ 

 of an inch (20 to 24 ft) in thickness. It is a strong membrane appearing 

 in the form of a clear zone in the mass of surrounding cells. It is marked 

 by striae, which are thought by some anatomists to indicate the presence of 

 small pores ; but the large, single opening called a micropyle, which is 

 found in many of the osseous fishes and in mollusks, has not been demon- 

 strated in the human ovum. 



Between the zona pellucida and the vitellus, is a narrow space, about 

 26 } 00 of an inch (1-3 ft) in diameter. This has been called the peri vitelline 

 space (Nagel). 



The vitellus is contained in the zona pellucida. It presents a clear, outer 

 zone -gTjVo to ^^5-5- of an inch (4 to 6 ft) in diameter. This can not be dis- 

 tinguished from the protoplasmic zone, except in perfectly fresh ova. It is 

 composed of clear protoplasm without granules and represents that portion 

 of the protoplasm of the vitellus which is not at any time converted into 

 deutoplasm (Nagel). Within the clear zone, is the protoplasmic zone 

 (formative yelk). This presents very fine granules, and the zone is -^-^ 

 to y^nr of an inch (10 to 21 ft) in thickness. Occupying the central por- 

 tion of the vitellus, is the deutoplasm (nutritive yelk), forming a mass about 

 g-J^j- of an inch (82 to 87 ft) in diameter. The deutoplasm presents granules 

 of different sizes and different refractive power. Treated with eosin, the 

 protoplasm becomes rose-colored, but the deutoplasm is unaffected. As the 

 ovum reaches its final stage of development, the protoplasmic zone, as far 

 as that portion which forms the so-called outer zone, is gradually changed 

 into deutoplasm. In Plate II, Fig. 1, an ovum is represented in which this 

 change is in progress. 



The germinal vesicle lies always in the protoplasmic zone, just out- 

 side of the deutoplasm. As the mass of deutoplasm extends, the germi- 

 nal vesicle is pushed toward the periphery of the vitellus. The vesicle 

 measures about 3-5^ of an inch (25 to 27 ft) in diameter. 

 It is globular, with a double contour. In hardened prepa- 

 rations, it presents a frame-work of fine anastomosing 

 fibres. In the fully developed human ovum, no amoeboid 

 movements have as yet been observed in the germinal 



Fi Q .v*.-p>-inwrdiai vesicle ( Na e1 )' In Plate IT >. Fi S' 2 > the germinal vesicle 

 ovum with two ger- i s se en Iving upon and not within the deutoplasmic zone. 



minal vesicles and J x . 



foincuiar epitheii- The mature ovum presents but one germinal vesicle. I wo 



um ; from the ova- . n . 



ry of a new-born germinal vesicles, however, are sometimes lound in primor- 



child (Nagel). ' 



dial ova (see Fig. 284). 



The germinal spot (Wagner) is contained in the germinal vesicle. Some 

 vesicles present two germinal spots. In perfectly fresh ova, the germinal 

 spots have been observed to undergo amoeboid movements. 



Discharge of the Ovum. A ripe Graafian follicle measures to of an 

 inch (10 to 12 mm.) in diameter, and presents a rounded elevation, contain- 



