ORIGIN OF THE CORPUS LUTEUM 145 



nor less than a network of these fibrils applied closely to the 

 base of the granulosa layer. 



The theca externa consists of a layer of long spindle-shaped 

 cells, shading off into the stroma of the ovary (or into the cap- 

 sular connective tissue, over that part of the follicle which is 

 jutting out from the ovary). It is composed chiefly of collage- 

 nous fibrils and their associated fibroblasts, but it is highly in- 

 teresting to note in connection with the subsequent collapse of 

 the follicle, that there are also a good many smooth muscle 

 fibers, as is readily seen by the use of Van Gieson's stain. There 

 are no elastic fibers, except in the walls of the larger blood- 

 vessels. 



Just before rupture there are many mitotic figures in the cells 

 of the theca externa, but only occasional signs of cell division 

 in the theca interna and the granulosa. 



Injected specimens show the blood- vascular distribution to be 

 as described by His and J. G. Clark (fig. 6). Large vessels form 

 a network in the theca externa, sending twigs inward to form 

 a generously anastomosing plexus which lies in the above- 

 described spindle-celled zone of the theca interna. 



I have found a curious arrangement of the blood-vessels in 

 the ovum-bearing area of the follicle. The discus proligerus is a 

 cone-shaped or rounded projection of the granulosa bearing the 

 ovum near its apex, which until shortly before maturation of the 

 ovum is composed of densely packed granulosa cells. At its 

 base, in this particular species, are found a number of little 

 vascular loops sprouting up from the vessels of the theca interna 

 well into the granulosa of the discus, and pushing before them the 

 cells of the basal columnar layer (fig. 6, loops). The basal cells 

 appear as if radiating from the loops, and like all the cells of 

 the area occupied by the loops are enlarged and have a much less 

 dense cytoplasm than the other granulosa cells. Those loops 

 which are near the center of the discus are longer than those 

 toward the periphery. Such vascular loops penetrating the 

 granulosa have apparently not been mentioned previously. 

 They are not to be found in the rat and mouse, the only other 

 species which I have studied in this regard. It would seem that 



