The drawings were made at table level with a Spencer camera lucida. For 

 the detailed drawings ocular 6 and Spencer 1.5 mm. apochromat N. A. 1.30 ob- 

 jective were used. For figures la to 11a ocular 2 and 16 mm. apochromat N. A. 

 0.30 objective were employed. For the most part the drawings were made from 

 sections 8 to 10 micra thick. 



PLATE 1 



EXPLANATION OF FIGURES 



1 Section through specimen 256 (early primary bud stage) showing a germ 

 cell lying between entodermic and ectodermic layers. The rectangle repre- 

 sented as figure la indicates the area from which this drawing was made. 



2 Detailed drawing from the area indicated in figure 2a (primary bud stage) 

 showing a germ cell and a large dividing cell joined to the entoderm by a thin 

 strand of tissue. 



3 Detailed study from specimen 290 (early secondary bud stage) showing 

 germ cells lying close to the entoderm among stray mesoderm cells of the primi- 

 tive streak area. 



4 Later secondary bud stage showing a section through one of the buds 

 (fig. 4a). 



358 



