ORIGIN OF VASCULAR TISSUES 91 



suggest, it is evident that if circulation could be prevented with- 

 out altering the normal process of blood-formation, a great deal 

 of light would be thrown on that normal process. Stockard (55) 

 employed alcoholic treatment as a means of preventing the cir- 

 culation of body fluids. He found from such study (64, p. 125) 

 that there are ''two distinct and limited places of origin" of red 

 blood cells — the stem-vein, and the posterior surface of the yolk- 

 sac. In his writings he repeatedly states in entire paragraphs of 

 italics that if there has been no blood-circulation, the following 

 regions and parts never contain a single erythrocyte in any em- 

 bryo at any age. These regions include: (1) all the anterior 

 blood-vessels, (2) all the anterior mesenchyme, (3) the anterior 

 3^olk-surface, (4) the heart, and (5) the liver. He claims that 

 leucocytes form only in the anterior mesenchyme of non-circu- 

 lating embryos. Later in the discussion I shall consider Stock- 

 ard's work in connection with my own; this statement of his 

 results will suffice to show the differences in our findings. 



1. Hybrid material 



Thorington and I (55) have shown that hybrid teleosts devoid 

 of circulation may develop erythrocytes in practically any region 

 of the body and of the yolk-sac. The embiyo from which our 

 figures 13 and 15 were taken is of great interest. The heart was 

 solid at both extremities, yet it contained erythrocytes. Per- 

 haps a blood-lacuna formed as a portion of the heart. The car- 

 diac tube was widely separated from ventral aorta by mesen- 

 chyme. The aorta was barren of blood-cells, yet the precardi- 

 nals contained many erythrocytes, as did the ducts of Cuvier. 

 No blood-cell ever entered the aorta from the cardiac tube. 

 The aorta itself was discontinuous. For further details see the 

 original communication (55). 



2. Chemically treated embryos 



The following section is devoted to a description of conditions 

 obtained by early chemical treatment of the developing ova of 

 Fundulus heteroclitus. The descriptions are based principally 



