614 



THE AMERICAN NATURALIST [Vol. XL 



walls, i. e., it is a syncytium whose outer and inner extremities 

 form the external and internal limiting membranes. This is 

 in accord with the conclusion of Bernard (:00). Early writers 

 described it as made up of discrete cells, while Cameron goes 

 to the opposite extreme and maintains that it consists of nuclei 

 with absolutely no cytoplasm at all. Cytoplasm there certainly 

 is in the chick at this stage if a cytoplasmic stain is used, but it 

 \ is almost imj)ossible to dem- 



^\ stain alone. It is difhcult, 



V • ' 'i'^ 'il'-^nt llu nu 

 . , :. i are evidently all ahkc 



