HISTOGENESIS OF BLOOD IN BUFO HALOPHILUS 213 



eosin or orange G and very intensely and tenaciously with iron 

 hematoxylin. When blood elements of later stages are stained 

 with Heidenhain's iron hematoxylin and eosin the granules of the 

 eosinophil leucocytes readily give up the black color and become 

 bright red. Bryce ('04) states that these granules were, in the 

 younger stages, either derived from, or actually were finely 

 divided yolk matter. 



At the 3-mm. stage some few of the cells are seen to be round- 

 ing up and detaching themselves from the mass. 



When stained with Dominici's eosin-orange G-toluidin blue, 

 the nuclei of these cells take on a deeper blue than those of the 

 mesenchyme, showing a finely reticular structure with dark blue 

 nodal points. Most of the cells contain one or two purple stained, 

 large, smoothly rounded nucleoli. With Wright-alcohol the 

 nuclei show the reticular structure even better, the reticulum 

 seeming more irregular. Chromatin particles lie at the nodes. 

 The karyoplasm is basophil, with a tinge of pink in some cells, 

 thus suggesting the faintly oxyphil condition of the later stages. 

 The cytoplasm is usually colorless or nearly so, becoming in- 

 creasingly basophil soon after, and contains many small brownish 

 black pigment granules, which are present throughout all the cells 

 of the embryo. 



The mesenchyme cell of this stage (3 mm.) is taking on a spindle 

 form. It has a basophil cytoplasm with fewer and smaller yolk 

 granules than the cells of the blood anlage. The nucleus is 

 clearer and poorer in chromatin, which lies in discrete, deeply 

 staining particles at the nodes of a loose network of lightly colored 

 linin threads. A deeply stained nucleolus is present. 



The cell of the blood anlage and the mesenchyme cell differ in 

 the reaction of the cytoplasm, in the number and size of the yolk 

 granules, and in the character of the nucleus. They are alike in 

 the possession of small dark brown pigment granules and in that 

 both are frequently seen in mitosis. 



