134 Embryonic Development of Ovary and Testis of Mammals 



persists after all the granulosa and inner theca cells and even the ovum 

 have entirely disappeared. It shows a more or less fibrous structure in 

 these later stages, finall}' disappearing without leaving a trace. The 

 above described closing-in of the follicular capsule stretches the con- 

 nective tissue strands joining the capsule with the theca externa. In 

 this manner, the cells of the intermediate theca interna are arranged 

 in radiating columns. These develop into the interstitial cells to be 

 described later. This view has already been advanced by Schottlaender, 

 91, Clarke, 98, Plato, 97, Limon, 02, and a number of others. 



At a stage immediately succeeding the disappearance of granulosa 

 cells and ovum, the nuclei of the still undeveloped interstitial cells be- 

 come amoeboid and then undergo a rapid process of amitotic division 

 (Plate VII, Fig. 27). This is not described in any of the literature, 

 although Dr. Frank E. Lillie and Dr. C. M. Child of this laboratory 

 both inform me that they have noted the same phenomenon. 



Van der Stricht, 01, finds that in the formation of the corpora lutea 

 of the bat (Vespertilio) the cells of the theca interna having taken on 

 the form of lutein cells, divide by mitosis for a short period, after which 

 division ceases entirely. Sobotta, 96, also has found scattered mitotic 

 figures in the theca interna of the rabbit after discharge of the ovum, 

 although he does not ascribe to this layer the formation of the lutein 

 cells. Eabl, 98, finds them to divide before the beginning of atresia, 

 not after that process has set in. 



After this process of amitotic division is completed the interstitial cells 

 rapidly increase in size and finally develop into the mature form in 

 which the cytoplasmic body is voluminous, clearly bounded, and stuffed 

 full of fat globules; the nucleus is enlarged and roimded; and a well- 

 defined centrosphere and centrosome have appeared. These interstitial 

 cells are similar to the lutein cells of the corpora lutea in all regards 

 save size. Even this criterion is not a safe one by which to distinguish 

 the two sets of elements. Certain interstitial cells of the ovary of a 

 6-months' old virgin, having become separated from the mass and lying 

 free in the loose stroma, are found to have enlarged to the dimensions 

 of the smaller lutein cells of the corpora lutea. 



Although the work of Sobotta, 96, Honore, 00, and others has led 

 them to assert that the lutein cells of the corpora lutea originate solely 

 from the granulosa cells of the discharged follicle, there are a large num- 

 ber of workers who hold the view that they originate solely from the cells 

 of the theca interna. Among such authors may be mentioned Clarke, 

 98, Van Beneden, 80, and Kolliker, 98. Van der Stricht, 01, and 

 Schulin, 81, consider them to arise from both sources. This question 



