100 FRANKLIN P. REAGAN 



In this embiyo the soUd distal end of a very feeble heart ends 

 blindly on a yolk sac the anterior portion of which is, and has 

 always been devoid of vascular tissues. Yet the anterior mesen- 

 chyme and the anterior vessels contain blood cells. As will be 

 shown later, the liver of this embryo contains erythrocytes, 

 though these may possibly be mesenchyme cells pushed out with 

 and included in the liver diverticulum. 



The conditions observed in figure 49 may now be considered 

 in section (figs. 65 and 66). In each case the position of the 

 blood-producing area is illustrated by solid black dots, while in 

 the illustrations of these regions more highly magnified the eryth- 

 rocytes are shown by unstippled cells. It is quite impossible to 

 do justice to the preparation by means of one-color illustrations. 

 The erythrocytes stained a brilliant red, the mesenchyme cells a 

 rich blue, while the probable transitional stages between the two 

 stained puiple. The erythrocytes seem to be identical in nature 

 with those in the intermediate cell-mass. Figure 65 shows a 

 section taken just posterior to the optic vesicles. The erythro- 

 cytes in this figure are not surrounded by endothelium; there is 

 a large group on the left side, and two groups on the right. The 

 latter are shown in greater magnification in figure 67, where in- 

 stead of the arbitrary black dots we have unstippled cells repre- 

 senting erythrocytes. Some of the cells surrounding this group 

 of erythrocyte groups seem to be flattening out to form endo- 

 thelium. 



In figure 66 we have a section through the dorso-median blood- 

 anlage observed in figure 49. These erythrocytes (fig. 68) lie in 

 a crevice in the fore-brain tissue; they are not surrounded by en- 

 dothelium, but are bounded entirely by ectoderm. No endothe- 

 lium developed in any region near this group of cells. It is even 

 doubtful whether one should find endotheUal tubes in this 'region 

 in the normal embryo at a stage corresponding to this. 



It is of interest to note that Professor McClure, working with 

 the fresh-water teleost Erim3''zon sucetta oblongus, has obtained 

 results similar to those above described for Fundulus. He ob- 

 tained chemically treated embryos without circulation, having 

 lacunae of erythrocjiies in the anterior mesenchyme. His ex- 



