HISTOGENESIS OF BLOOD IN BTJFO HALOPHILUS 211 



In birds (Danchakoff, '08 a) and reptiles (Jordan and Flippin, 

 '13; Danchakoff, '16 a) the primitive blood-cell is morphologically 

 a large lymphocyte and the primitive erythropoiesis gives way 

 gradually to the definitive. While in Selachia (Maximow, '10 a), 

 Dipnoi (Bryce, '04), Amphibia (Mietens, '10), and Mammalia 

 (Maximow, '09 a) the primitive blood-cell is a distinct form and 

 the formation of primitive erthrocytes is separated by an interval 

 from that of the definitive cells. 



Schridde ('07, '08), in human embryos of 1 to 13 mm., finds 

 that the first blood-cells all differentiated into nucleated erythro- 

 cytes, whose nuclei began to fragment in the 6-mm. stage. Later, 

 when blood formation in the liver commences, parenchyme cells 

 give rise tomyeoblasts, giant-cells, and erythroblasts, lymphocytes 

 not appearing until much later. 



Van der Stricht ('91, '92, '95, '99), in mammals and birds, and 

 Weber ('07 a, b), in birds, find that all the first blood-cells become 

 erythrocytes and that no white cells occur in the blood stream 

 at first. 



Stockard ('15 a, b) asserts that in Fundulus embryos without 

 circulation erythrocytes, endothelium cells, and leucocytes all 

 have distinct origins, no white cells being formed intravascularly 

 and all the first blood-cells arising from a definite anlage and 

 passing over into erythrocytes, and are not interrelated, no blood- 

 cells being formed from endothelium. He observed red cor- 

 puscles outside of the anlage, but accounted for them by assuming 

 a temporary circulation. White cells, on the other hand, arise 

 from the general mesenchyme. Reagan ('15 b, '17) and Reagan 

 and Thorington ('15) found that all the body mesenchyme of 

 Fundulus could furnish both blood- and endothelium' cells. 



MATERIAL AND METHODS 



My material consisted of eggs and larvae of Bufo halophilus 

 B. and G., from the closing of the neural groove to the beginning 

 of the metamorphosis. In this study only the earlier stages, up 

 to 19-mm. body length, are treated fully. The larvae were fixed 

 in Zenker-formalin for four to six hours, ten parts of formalin to 



