ORIGIN OF BLOOD AND ENDOTHELIUM 309 



Van der Stricht ('94). His studies were especially confined 

 to the mammals. As has often been the case the conclusions 

 reached from this pioneer study are largely correct in the light 

 of recent investigations. Van der Stricht held that the first 

 blood cells arising within the area vasculosa are entirely young 

 red cells, erythroblasts. When one surveys the literature of 

 this subject, it is found that all authors with three or four 

 recent exceptions (Bryce ('05), Dantschakoff ('07) and Maximow 

 '09), hold that the blood islands give rise exclusively to red, 

 haemoglobin bearing corpuscles, erythroblasts or finally erythro- 

 cytes. This is true for the Fundulus embryos described in this 

 paper and even though the cells are confined to their place of 

 origin and never flow away, since there is no circulation, yet the 

 groups always consistently contain only erythrocytes. 



Van der Stricht holds that the leycoblasts and leucocytes are 

 independent of the erythroblasts and arise extra-vascularly in 

 the mesenchyme and later wander into the vessels. 



Browning ('05) and Goodall ('07) have both recently claimed 

 that the leucocytes have a different origin from the erythrocytes 

 and arise at a later period. Goodall states: 



When leucocyte proliferation in the liver has begun, the islands of 

 erythroblasts and leucoblasts are definitely separate in position, and 

 the distinctness of their identity is obvious, and no transitions between 

 them can be seen. These facts argue strongly against the view that the 

 erythroblasts are derived from the primitive leucoblasts. 



Jolly and Acuna (^05) have pointed out that in early stages 

 only red cells are found in the blood. The first lymphocytes occur 

 very late and still later the granulocytes, so that the guinea-pig 

 embryo has attained a length of sixteen mm. before white blood 

 corpuscles are present. 



Again all authors with few exceptions seem entirely agreed 

 that the leucoblasts arise much later than the erythroblast. 

 All without exception also agree that the leucoblasts arise extra- 

 vascularly while the erythroblasts arise partially within the 

 sinuses, and that the island groups of erythroblasts soon become 

 surrounded by vascular endothelium while no vessel walls have 

 ever been described to form around the groups of leucoblasts. 

 These facts are no doubt of much genetic importance. 



