58 



COMPARATIVE PHYSIOLOGY. 



cavity (germinal ridge), wliich give rise to the ovum itself, and 

 the other cells surrounding it in the Graafian follicle. At first 



these inversions form 

 tuhules {egg-tubes) which 

 latter hecome broken up 

 into isolated nests of 

 cells, the forerunners of 

 the Graafian follicles. 



The Graafian follicle 

 consists externally of a 

 fibrous capsule' {tunica 

 fibrosa), in close relation 

 to which is a layer of cap- 

 illary blood-vessels (fu- 

 nica vasculosa), the two 

 together forming the gen- 

 eral covering (jtunica 

 propria) for the more 

 delicate and important 

 cells within. Lining the 



Fig. 57. — Section through portion of the ovary of . . . i <> n 



mammal, illustrating mode of development of tuniC IS a layer 01 Small, 



the Graafian follicles (Wiedereheim). 2), dis- ort*viaTitrTiQ+ ^n'Ki^ol ^^lla 



CUB proligerns ; Ei. ripe ovum; 6, follicular somewnai ouDicai ceiii 



"i"rerS'Te's?ciTTeistan°d'gSfn^i irnemhrana granulosa), 



spot (nucleolus) ; KE, germinal epithelium; ^bich at one part invest 

 Lf, liquor folliculi; Mg^ membrana or tunica ^ , 



granulosa, or follicular epithelium; Up, zona the OVUm Several layers 



epithelium, ovarian tubes, by means of which deep {ulSCUS proligerus), 



some of the nests retain their connection with -^n-vn^. +'U« -wrtw^o^-ni^o^ nf 



the epithelium; 5. cavity which appears with- wniie tne remamaer OI 



in the Graafian follicle; So, stroma of ovary; •jjjjg sDace is filled bv a 



iy, theca folliculi or capsule ; U, primitive „.,,. j7 7tt 



ova. When an ovum with its surrounding fluid (llQUOr JolllCUll) 

 cells has become separated from a nest, it is i i i . .i , j 



known as a Graafian follicle. probably either secreted 



by the cells themselves, 

 or resulting from the disintegration of some of them, or both. 



In viewing a section of the ovary taken from a mammal at 

 the breeding-season, ova and Graafian follicles may be seen in 

 all stages of development — ^those, as a rule, nearest the surface 

 being the least matured. The Graafian follicle appears to pass 

 inward, to undergo growth and development and again retire 

 toward the exterior, where it bursts, freeing the ovum, which is 

 conducted to the site of its future development by appropriate 

 mechanism to be described hereafter. 



Changes in the Ovum itself.— The series of transformations 

 that take place in the ovum before and immediately after the 



