66 B. F. KINGSBURY 



constitute the characteristic tissues of the ovary. The earUest 

 parenchymal growth^as usually termed, the medullary cords, 

 constituting the first proliferation — occupy therefore the center 

 and mediastinal portion of the ovary. The medullary cords at 

 first are free from distinguishable germ cells, although later 

 definite ova seem to appear in their midst. Later proliferations 

 from the surface epithelium produce cell cords in which the 

 reverse of the conditions characteristic of the medullary cords 

 holds — the germ cells become the dominant cells and the indiffer- 

 ent cells are distinguishable with difficulty. The differential 

 growth of the ovary is centrifugal, and hence older stages of 

 the oogenesis are more centrally located. The zone of oogonial 

 multiplication is peripheral, the proliferation of new oocytes ceas- 

 ing soon after birth. Connection of the egg cords with the sur- 

 face epithelium becomes lost two to three weeks after birth, and 

 by separation of the oocytes composing the outer portions of 

 the egg cords, resting or primary follicles are formed, marking 

 out a definite cortex. While the peripheral growth changes are 

 leading to the establishment of the definite cortex, within the 

 medulla the differentiation takes the form of follicle-formation. 

 The first follicles are apparently formed within the medullary 

 cords themselves, later ones include ova derived from the inner 

 portions of the egg cords. The early or medullary follicles are 

 very irregular and largely pluri-ovular. The follicle formation 

 follows the general plan of centrifugal differential growth, so 

 that, in general, less advanced follicles are more peripherally lo- 

 cated. Many of the large, irregular pluri-ovular follicles attskin 

 a marked development so that in old kittens with the greatest 

 development of these follicles the ovary reaches a size greater 

 than at a subsequent period, since these, as well as all the early 

 formed medullary follicles degenerate. Such degeneration is 

 particularly profound as sexual maturity is approached, although 

 degenerations are constantly present in the ante- and postpartum 

 periods, in less mature ovaries, and subsequently throughout 

 the period of sexual maturity. The degenerations of the pre- 

 sexual period are of a somewhat different type. The early med- 

 ullary follicles degenerate; later ones that attain a large size as 



