114 THE PHYSIOLOGY OF REPRODUCTION 



vesicles of various sizes, each with an ovum, surrounded by an 

 epithelium. These are called Graafian follicles. Certain other 

 structures, consisting of very large yellow-coloured cells en- 

 closed by a branching network of connective tissue, are also 

 often found. These are the corpora lutea or discharged folUcles 

 to be described more fuUv later. The stroma contains, further, 

 a varying number of epitheloid interstitial cells. 



In order to gain a proper understanding of the structural 



V 



Fig. 19. — Section through ovary of cat. (From Schron.) 



1, Outer surface; 1', attached border; 2, fibrous central stroma; 3, peri- 

 pheral stroma ; 4, blood-vessels ; 5, young follicles ; 6, 7, 8, 9, and 9', 

 larger developing follicles; 10, corpus luteum. 



and functional relations of the different parts of the ovary, 

 it is necessary to make some study of its developmental history. 

 Pfliiger ^ appears to have been the first to regard the ova ^ 

 and epitheUal cells of the Graafian folhcles as originating either 

 in the form of ingrowths simulating tubular glands, or as sohd 

 columns of cells from that embryonic layer which Waldeyer 

 afterwards designated the germinal epithehum. The tubular 

 ingrowths had aheady been noticed by Valentin,^ who, however, 



^ Pfliiger, Veher die Eierstockc der Sdugethiere und des Menschen, Leipzig, 

 1867. 



^ The mammalian ovum was discovered by von Baer (Ueber Entwicke- 

 lungsgeschichte der Thiere-Seobaefitung und Reflexion, vol. i. , Konigsberg, 1828). 

 In 1861 Gegenbauv showed that the vertebrate ovum was a single cell. 



' Valentin, " Ueber die Entwickelung der FoUikel in dem Eierstooke der 

 Saugethiere," Mutter's Arch,, 1838. 



