STRUCTURE OF THE OVARY. 167 



cumstance that in a large number of ovaries the epithelium lining 

 the Fallopian tube is continued directly into the epithelium 

 covering the ovary, except that the cells no longer bear cilia. 



The ovaries of Amphibia, Osseous Fishes, and Cyclostomata have no 

 germ- epithelium investment, the explanation of which will be subse- 

 quently given. I have not at present been able to make any observa- 

 tions upon the Ganoids and Sharks. 



Graafian follicles of various size are in part indistinctly 

 visible through the superficial layers of the ovary, and partly 

 project, in the form of translucent hemispherical elevations, to a 

 greater or less extent beyond the general level, surrounded by, 

 for the most part, a very narrow-meshed plexus of vessels 

 perceptible even to the naked eve. Between these a few 

 "corpora lutea" may be seen, which are ovisacs, in a con- 

 dition of retrogression or atrophy. A vertical section, as at 

 a, in fig. 191, exhibits the germ-epithelium, beneath which is a 

 layer of connective tissue, itself composed of several subor- 

 dinate and decussating layers, in which are found a few ovarial 

 tubes (b 6), and young ovisacs (c c). To this succeed more 

 mature ovisacs, some of which' contain nearly ripe eggs ; and 

 lastly, the highly vascular hilus stroma, that is commonly 

 described as medullary substance, in contradistinction to the 

 above-mentioned layers that are collectively regarded as the 

 cortical substance. The term parenchymatous zone zo-na 

 parenchymatosa might be distinctively applied to the cor- 

 tical layer ; and that of vascular zone zona vasculosa to the 

 medullary substance. The ovaries of adult Mammals, of Man, 

 and essentially also of all Birds, Reptiles, and Sharks, are 

 constructed on this general type. In the latter classes, and 

 especially in Birds, the organ becomes divided on the one hand 

 by deep constrictions into several closely applied lobules, whilst 

 on the other, from the number and size of the mature ovisacs, 

 which ultimately hang by short stalks from the surface, it 

 assumes a grape-like appearance, that at first sight appears to 

 indicate a profound distinction between them and the com- 

 t form usual in the ovaries of Mammals. 



I must expressly state, however, that the above account only 



