FEMALE ORGANS OF GENERATION. 491 



Sometimes two ova are found in a Graafian vesicle (Bischoff, 1 

 Davaine 2 ). This ovum is composed of a cellular envelope 

 or mtelline membrane (or chorion, D), having protoplasmic 

 contents or yelk (vitellus} (Fig. 135, C) ; we must not, how- 

 ever, confound this yelk with the entire yellow part of a 

 bird's egg ; the latter contains the egg of mammalia, as its 

 tread or cicatricula, andj in addition, a great mass of nutrient 

 material, the yellow, properly so called ; a nucleus or ger- 

 minal vesicle (B), which contains inside a nucleolus or ger- 

 minal spot (A), is always found in the vitellus. 



Not all the Graafian vesicles of an ovary arrive simulta- 

 neously at this degree of development, nor do they contain 

 all their ova in a state of maturity. 



It is only at the commencement of the period of puberty, 

 or, more correctly, at each menstrual period, that one or two 

 ovisacs (Graafian vesicles) are perfectly developed. At this 

 time one of the Graafian vesicles, usually that next the sur- 

 face of the ovary, is swollen, its contents augment, and it be- 

 comes more marked ; that portion of its wall nearest the sur- 

 face of the ovary presses against this surface ; at this point 

 occurs an arrest of nutrition, and consumption of its own 

 walls; this condition, assisted by an increasing swelling of 

 the central portion of the ovary (sir oma or spongy portion 

 of the ovary) readily induces a rupture of such a nature that 

 the contents of the ovisac escape, bringing out the ovum with 

 the debris of the proligerous disc. Usually this is the most 

 favorable moment for fecundation of the ovum by the arrival 

 of the spermatozoids, if, perchance, these latter have been 

 introduced into the female genital organs; but whether the 

 ovum is, or is not fecundated, the appendages of the uterus 

 act, in a mechanical point of view, almost in the same man- 

 ner. 



After the expulsion of the largest part of its contents, the 

 Graafian vesicle closes again and undergoes a cicatricial 

 healing of its ruptured envelope, leaving but a slight trace of 

 its rupture ; it has also a yellow color received from the blood 

 pigment, arising from a slight hemorrhage which accompanies 



1 Bischoff, " Traite du Developpement de 1'Homme et des 

 Mammiferes," suivi de 1'histoire du developpement de 1'oeiif du 

 lapin. Translated from the German by A. J. L. Jourdan. Paris, 

 1843. 



2 Davaine, " Memoires sur les Anomalies de 1'CEuf." Paris, 

 1801, 8vo, with illustrations. 



