208 WILLIAM WALLACE. 



mammalian t^'-pe^ — then the development of this body in 

 Spinax must be a very slow process indeed, taking- many 

 months for its completion, whereas the whole process in the 

 mouse takes about three days. 



I am inclined to think that the more advanced corpus 

 luteum is undergoing degeneration. The signs of this 

 are — (1) The disintegration of the inner cells of the 

 follicular epithelium and the presence of free nuclei from 

 this source in the cavity. These nuclei are obviously 

 degenerating. 



(2) The appearance of the nuclei in the theca. Some of 

 these are degenerating; others are dividing amitotically 

 (fig. 33). I may add that I have never seen karyokinesis in 

 any of the cells of the corpus luteum of Spinax^ either in 

 the early or in the advanced stage. I am not, however, 

 prepared to say that karyokinesis does not occur in the earlier 

 sfcao*es, as I have not examined a sufficient number of sections. 



(3) Degeneration of the fibres in the theca. 



If, then, as the above observations seem to indicate, the 

 corpus luteum we are considering has reached its maximum 

 development and is now on its wa}^ to degenerate, it is clear 

 that the structural changes which take place in the ruptured 

 follicles of this Elasmobranch, while they present a distinct 

 approach to the conditiom in mammals, are much less pro- 

 found and complicated. 



The corpus luteum of Spinax is likewise much simpler 

 than that of Myliobatis according to the descriptions and 

 figures Giacomini gives of the latter. The corpus luteum of 

 Myliobatis is represented as a more oi" less solid body, in 

 which the interpenetration of the follicular epithelium by 

 trabecula) of connective tissue and blood-vessels has taken 

 place on a large scale so that the corpus luteum looks like 

 "a glandular organ full of epithelial tubes." In Spinax, 

 on the other hand, the invasion of the epithelium by the 

 connective tissue in the most advanced stage of the corpus 

 luteum available for examination has only proceeded to a 

 very slight extent. 



