HISTOGENESIS OF BLOOD IN BUFO HALOPHILTJS 217 



pig often amoeboid. The nucleus is large, surrounded by a 

 narrow cytoplasm. It is round or slightly indented. Within 

 it are pale karyosomes and one or more large distinct nucleoli, 

 which stain with a reddish tinge with eosin-azure II or Dominici's 

 stain, lying on a linin net. The cytoplasm is very finely retic- 

 ular and fairly strongly basophil, more so than the cytoplasm 

 of endothelium and mesenchyme cells. It contains clear round 

 vacuoles, lying singly or in small groups. The nucleus is usually 

 somewhat eccentric, with its indented side toward the broader 

 part of the cytoplasm. On this side close against the nuclear 

 membrane lies a very distinct, usually hemispherical attraction 

 sphere, staining red with eosin-azure II or Dominici's stain. 

 Around this lie many vacuoles. In iron-hematoxylin prepara- 

 tions a typical pair of centrosomes takes the place of the sphere. 

 Many mitotic figures are found in these cells. Thus it may be 

 seen that the nuclei are readily comparable in mammals and in 

 Amphibia. The difference in the degree of basophilia in these 

 forms may probably be attributed entirely to the presence and 

 gradual digestion of yolk in the cytoplasm, for when the primi- 

 tive blood-cells in Bufo halophilus have lost their yolk and have 

 differentiated into red and white cells, both types show a more 

 or less basophil cytoplasm (fig. 3). In birds and reptiles (Dan- 

 chakoff, '08 a, '16 a; Jordan and Flippin, '13) the primitive blood- 

 cells are morphologically large lymphocytes, amoeboid, spherical, 

 with a more or less broad basophil cytoplasm. They have a 

 large clear nucleus, which may be indented, with one or two 

 well-marked, somewhat metachromatic nucleoli and well-marked 

 chromatin particles. The nucleus is excentric and a centriole 

 may be present. So, in the Sauropsida the primitive blood-cells 

 are large lymphocytes, while in Dipnoi, Amphibia, and Mammalia 

 they are a morphologically distinct form. They are neither red 

 cells, nor are they white cells of any adult type. Their nuclei 

 are in B. halophilus distinct in character from those of the prim- 

 itive erythrocytes. 



