462 CHARLES H. SWIFT 



This stage of 8 days is the beginning of a period of rapid 

 multiplication of the germ-cells, which reaches its height, as will 

 be described later, during the 9th and 10th days, but which con- 

 tinues with decreasing activity for some days longer. 



CORTICAL CORDS AND ORIGIN OF THE DEFINITIVE SEX-CELLS 



The 8th, 9th, 10th and 11th day stages may be described to- 

 gether, since they are characterized in common by one fact, 

 that is, germ-cell division. 



As has been mentioned from time to time, as the various 

 stages were being described, there has been little change in the 

 germ-cells. Their size has remained constant, as has that of 

 their nuclei and spheres. The vitellus, which they acquired 

 from the germ-wall entoderm, although constantly diminishing 

 in quantity, has been easily seen up to this stage. Their rel- 

 atively constant size and ever present vitellus have been due to 

 a lack of division. These facts have been remarked by all 

 describers of them but Rubaschkin especially, in the guinea pig, 

 has accentuated their primitiveness. 



At 8 days the primordial germ-cells in the germinal epithelium 

 are more numerous than in previous stages. In one section 18 

 germ-cells were present in the epithelium. The majority still 

 have a little vitellus but in some cells this is absent. They are 

 present in the deeper portions of. the epithelium next the slight 

 quantity of connective tissue, which separates the medullary 

 region from the germinal epithelium. This connective tissue is 

 the primordial albuginea. Most important, however, as far as 

 the germ-cells are concerned, some are in a state of division. In 

 one 8-day embryo 7 dividing primordial germ-cells were counted. 



At 9 days the primordial germ-cells are actively dividing. 

 Little groups of 3 and 4 with karokinetic figures are found in the 

 deeper parts of the germinal epithelium (fig. 7) . The lower part 

 of the epithelium, next the albuginea and medulla begins to have 

 a lobulated appearance as has been described by d'HoUander 

 ('04) and Firket ('14). These lobulations are due to the groups 

 of germ-cells, just described, and elements resembling those of 

 the more superficial layer, and are the first evidence of the cortical 



