454 



CHARLES H. SWIFT 



but in greater measure to an increase in the amount of the under- 

 lying tissue (fig. 2). 



As regards the primordial germ-cells, there has been practi- 

 cally no change in their appearance; however, their distribution 

 is quite different from that described in the last stage. Although 

 a majority are in the medial portion of the gonad, yet they are 

 not grouped as in the preceding embryo, but they are more evenly 



pro. 

 germ.ep. ' 





Fig. 2 Portion of a transverse section through indifferent gonad of a 4-day 

 chick embrj^o, to show the thick germinal epithelium, and primordial germ-cells, 

 one of which is dividing — a rare occurrence at this stage. 



distributed in that portion of the epithelium and mesenchyme 

 near the mesentery. This change in position can be accounted 

 for by growth of the gonad and to a certain extent by their power 

 of amoeboid movement. The germ-cells are not entirely qui- 

 escent for in the seven embryos studied about a dozen were found 

 dividing (fig. 2). That some division is taking place is also 

 evidenced by the fact that an occasional group of 8 to 15 of them 

 are found in which the cells are solely germ-cells without any 

 tissue whatever between, indicating that a number of successive 

 mitoses had probably occurred. 



