94 8 



THE OVUM. 



of puberty. The maturing follicles (IV) at first sink more deeply into the stroma 

 of the ovary, become distended by taking up water (liquor folliculi), acquire 

 a vascular, independent well-differentiated capsule (theca folliculi), and their 

 epithelium (IV , g) (membrana granulosa) increases through mitosis in a similar 

 manner, to form a layer of several rows of small cells. In the last stages of ripen- 

 ing the follicle leaves the depths of the stroma, again to reach the surface: it now 

 attains a diameter of from i to 1.5 mm. and is ready to rupture. Only a 

 small number of Graafian follicles attain normal final development; the majority 

 previously undergo atrophy. In some animals (rabbits) the occurrence of furrow- 

 ing has been observed as a noteworthy phenomenon. 



The medullary substance, which extends from the hilus into the interior 

 of the ovary, consists of vascular, fibrous connective and elastic tissue, with 

 bundles of unstriated muscle-fibers; in contradistinction to the cortical sub- 

 stance, which contains principally cellular connective tissue, with the epithelial 

 constituents in various stages of development. The ovary possesses numerous 

 nonmedullated nerves (connected with sympathetic ganglia) , of which the majority 

 terminate in the walls of the vessels (also the capillaries), and others between the 

 folliclesjand upon their surface. 



Germinal spots. 



Accessory nucleoli, .. 

 (also /.) 



Cells of discus proligerus (oophorus). 



Yolk. 



Hit Zona pellucida. 



FIG. 357- Mature Rabbit Ovum (after Waldeyer). 



m According to Paladino the ovary of woman is in a state of continuous involu- 

 tion and true new-formation through invagination of the germinal epithelium. 

 According to Waldeyer the mammalian ovum is not a simple cell, but a more 

 complex structure. The original ovular cell, he believes, is formed only from 

 the germinal vesicle and germinal spot, and the surrounding clear unencap- 

 sulated portion of the yolk (Fig. 358, ///). The remaining portion of the yolk 

 is derived from transformed granulosa-cells, which also constitute the zona pel- 

 lucida. 



In animals the following peculiarities may be observed in the formation of 

 OV ?- m -j st ovular cell s are known as primitive ova or ovogonia. 



divide several times by mitosis at first into small, then into larger ova- 

 >tner cells or ovocytes. These mature and after undergoing division by mitosis 

 I or twice give rise to the polar bodies and thus form the true fully devel- 

 oped ovules. 



Holoblastic and Meroblastic Ova. The ova of batrachians and cyclostomata 



are formed according to the same type as those of mammals. They are designated 



holoblastic ova, because their contents are entirely transformed into the forma- 



that serve for the development of the embryo. In contrast with these, 



birds monotremata among mammals, reptiles, and the remaining fish have so- 



ca led meroblastic ova. These contain, in addition to the (white) formative 



yolk, which corresponds to the yolk of holoblastic ova, and yields the embryonal 



cells, also the so-called nutritive yolk (yellow in birds), which serves as a source 



the embryo during the period of development. This nutritive 



