OVARIES IN TRLEOSTRAN AND ELASMOBRANCH FISHES. 207 



the sheep is confirmatory, in the main, of Sobotta's observa- 

 tions. Marshall, however, records occasional karjokinesis of 

 the follicular epithelial cells. He also maintains that the 

 theca externa, as well as the theca interna, g'rows 

 inwards between the epithelial cells, whereas Sobotta has 

 stated that only the theca interna is involved in the 

 process. 



From a study of two stages in the development of the 

 corpus luteum in Spinax, I can confirm Sobotta's observa- 

 tions in reg-ard to the following points: — (I) Hypertrophic 

 enlargement of the cells of the follicular epithelium ; (2) in- 

 growth of the connective tissue of the theca at various points 

 in a radial manner; (3) ingrowth of blood-vessels along 

 with the connective tissue. These things are illustrated in 

 figs. 31, 32. 



The doubtful and difficult point to determine in the case 

 of Spinax is this: — Whether the corpus luteum of the 

 advanced stage, which is no doubt some months and may be 

 a year old, represents a stage in the formation or a stage in 

 the degeneration of the corpus luteum, Sobotta could find 

 no evidence of degeneration in any of the corpora lutea 

 of the mouse. 



Giacomini (1896) also states, in regard to Myliobatis 

 bovina, that the corpus luteum does not degenerate, but 

 remains as a permanent structure in the ovary. 



I have said that the cavity of the corpus luteum of the 

 second or more advanced stage in Spinax is filled with 

 blood-cells derived from the veins in the theca. These veins 

 grow inwards radially with the strands of connective tissue 

 (fig. 31). Amongst the red blood-corpuscles in the central 

 cavity may be seen leucocytes and nuclei, some of which 

 appear to be derived from the theca, and others from the 

 follicular epithelium. Whether subsequently the blood in 

 the central cavity is absorbed and a core of connective tissue 

 formed in its place, as in the mouse, I cannot sa3^ If so — 

 that is to say, if the stage we are considering in Spinax is 

 an early one in the formation of a corpus luteum of the 



