508 CHARLES H. SWIFT 



cell in particular is found in the heart. It must have moved in 

 through the vessels by its own amoeboid properties, since the 

 heart, in an embiyo of this age, has not as yet begun to propel 

 the blood. In fact this cell has a marked amoeboid appearance. 



In embryos with 9 and 6 somites respectively the primordial 

 germ-cells are all anterior and antero-lateral in respect to the em- 

 bryo proper. Most of the germ-cells are present in the space 

 between germ-wall entoderm and mesoderm. The few present in 

 the mesodermal spaces have reached that position by migration 

 from the former position. Some are present in the space between 

 ectoderm and mesoderm; they have either passed through the 

 mesoderm from the space between entoderm and mesoderm or 

 have been left in that position by the outgrowth of mesoderm. 



These germ-cells at this age have the large attraction-sphere 

 so often referred to, as well as the abundant yolk. The nucleus 

 is not so large as in older germ-cells and the chromatin does 

 not exist in the two definite masses. Instead it is more evenlj^ 

 scattered throughout the nucleus and in some is reticular in 

 appearance. 



The germ-cells are very conspicuous, as, either isolated or in 

 groups of two or three, they lie in the space between entoderm 

 and mesoderm. 



Fig. 7 Portion of a transverse section through a 21 somite chick embryo at the 

 level of the 20th somite. Meves' fixation and Meves' iron-hematoxylin stain. 

 X 1125. pr.o., primordial germ-cell; vit., sphere of vitellus or yolk material; sp.w., 

 splanchnic mesoderm; hl.v., lumen of blood vessel. 



Fig. 8 Portion of a transverse section through a 21 somite chick at the level of 

 of the 18th somite. Meves' fixation and Meves' iron-hematoxylin stain. X 1125. 

 pr.o., primordial germ-cell; ?iuc., nucleus of primordial germ-cell; sp.m., splanchnic 

 mesoderm; hl.v., lumen of blood vessel; end., nucleus of endothelial cell. 



Fig. 9 Portion of a transverse section through a 21 somite chick embryo at the 

 level of the 21st somite. Meves' fixation and Meves' iron-hematoxylin stain. X 

 1125. pr.o., primordial germ-cell; sp.m., splanchnic mesoderm; bl.v., lumen of 

 blood vessel; ent., entoderm. 



Fig. 10 Portion of a transverse section through a 21 somite chick embryo at the 

 level of the 19th somite. Meves' fixation and Meves' iron-hematoxylin stain. X 

 1125. pr.o., primordial germ-cell; pr.'o.', primordial germ-cell dividing; .sp.?n., 

 splanchnic mesoderm; 6^1)., lumen of blood vessel; end., nucleus of endothelial 

 cell; ent., entoderm. 



