466 CHARLES H. SWIFT 



tached by a constricted portion or neck. Between the lobulations 

 there is much connective tissue, which is also present between 

 the medulla and the superficial region which may be called the 

 cortex. 



The medullary region at this time has a rather striking appear- 

 ance due to the large cavities in the deeper portions of the med- 

 ullary cords. These large spaces have unstainable contents 

 since they never show an}- evidence of stain. 



This 10-day stage is of special interest because it was at this 

 stage that d'HoUander ('04) began his study of oogenesis in the 

 chick. At this stage of development according to d'Hollander, 

 the cortical region consists of two zones, the layer of superficial 

 indifferent cells or epithelial layer, and the deeper layer of 

 germinative buds, which later become the cortical cords. 



The epithelial layer is made up of cylindrical cells, with 

 elongated nuclei and long axes directed perpendicularly to the 

 surface of the ovary. 



The germinative buds are made up of several types of cells. 

 One kind, which he calls indifferent deep cells, is scattered 

 irregularly throughout the buds. According to d'Hollander, 

 these cells resemble the superficial indifferent cells from which 

 they are derived. The deep indifferent cells give rise to oogonia 

 of two kinds a and a. The oogonia of type a are true oogonia, 

 those of type a are intermediate in character, resembling, on the 

 one hand, the deep indifferent cells, and on the other, the true 

 oogonia. The deep indifferent cells may also by division produce 

 follicular cells, which at this stage cannot be distinguished from 

 the parent cell. D'Hollander's scheme is as follows: 



Superficial indifferent cell 



/ \ 



Superficial indifferent cell Deep indifferent cell 



. /\ 



Follicular cell \ 



Oogonia a and d 



