tmr;: 





Fig. 3 Portion of a transverse section through the twentieth somite of a 25 

 somite embryo; same embryo as figure 4, for which this figure is the key-plate. 

 Meves' fixation and Meves' iron-hematoxylin stain. X 120. pro., primordial 

 germ-cell in small blood vessel of splanchnic mesoderm; nwc, nucleus of primor- 

 dial germ-cell; at.sp., attraction-sphere of primordial germ-cell; bl.c, blood cell 

 in blood vessel; sp.m., splanchnic layer of mesoderm; so.m., somatic layer of 

 mesoderm; ao., aorta; ent., entoderm; ect., ectoderm; Wd., Wolfiian duct; neph., 

 nephrotome. 



Fig. 4 Portion of a transverse section through the twentieth somite of a 25 

 somite embryo; this figure is drawn from the same embryo as figure 3 and is a higher 

 magnification of the marked off region. Meves' fixation and Meves' iron-hema- 

 toxylin stain. X 1125. pr.o., primordial germ-cell; nuc, nucleus of germ-cell; 

 at.sp., attraction-sphere of germ-cell containing a centrosomc; bl.c, blood-cell; 

 ent., ei toderm; sp.m., splanchnic mesoderm. 



503 



