156 José F. Nonídez 



Ab str at 



The present paper is based on a study of developing and adult ova- 

 ries. The chief conclusions reached are the following: 



1. The interstitial cells (Figs. I and 4, i\ Fig. 2, /í, B) are a constant 

 eature in all the ovarles examined and can be readily distinguished from 



other cells on account of their much vacuolated cytoplasm and round, 

 deeply staining nucleus. As shown by Firket these cells are modified 

 epithelial elements, arising in the degenerating sexual cords in the me- 

 dullary zone of the ovary (Fig. 3, i). They begin to appear about the 

 twelfth day of incubation, showing the same characteristics as those pre- 

 sent in the adult where they form clusters surrounded by a basement 

 membrane and a thin layer of connective tissue cells. 



2. Interstitial cells of lymphoid origin (Fig. 2, C) homologous with 

 the intertitial cells in the testis, described in a preceding paper, also occur 

 in the ovary. They appear scattered through the stroma and seldom 

 collect in groups around the blood-vessels. They arise, as those in the 

 testis, from small lymphocytes (Fig. 5). 



3. The writer has not been able to confirm the presence of the se- 

 cond variety of interstitial cells described by Firket in the embryo of the 

 eighteenth day and suggests that those elements are either interstitial 

 cells of the lymphoid type or hypertrophied connective tissue cells laden 

 with fat droplets. 



4. The last section of the paper is devoted to a discussion of the 

 probable physiological meaning of the interstitial cells. 



The so-called corpus luteum of the fowl, which according to Pearl and 

 Boring arises from the interstitial cells, is compared with the mammalian 

 corpus luteum. In the latter as a result of processes of differentiation a 

 new morphological unit is formed; the cells of this new structure differ 

 greatly from the interstitial cells and from those in the foUicular epithe- 

 lium, both of which have been regarded as the source of the corpus lu- 

 teum. In the fowl all the changes leading to the formation of yellow 

 spots in the discharged follicles are essentially degenerative, as shown by 

 the fusión of the cytoplasmic vacuoles and the shrinkage of the nucleus. 

 In the opinión of the writer a corpus luteum does not occur in the fowl. 



