110 FRANKLIN P. REAGAN 



tains no trace of a heart except an exceedingly minute vestige of 

 its arterial 'insertion' which can be seen only in section. The 

 erythrocytes visible in the living condition are conventionally 

 represented by means of black dots. A column of erythrocytes 

 formed in the intermediate cell-mass. Endothelial cavities, 

 many of which were surrounded by pigment cells, are represented 

 as dark ramifications on the yolk. There are no continuous 

 channels. Large numbers of erythi'ocytes developed in the im- 

 mediate region of the pericardium, and some developed beneath 

 its mesothelial lining; no erythrocytes or endothelium developed 

 on the posterior yolk-surface. Sections of this embryo reveal no 

 connection of systemic and yolk-sac vessels. Ducts of Cuvier, 

 as well as vitelline veins, are absent. The posterior yolk is seen 

 in section to be quite free of vascular tissue. Owing to the.trans- 

 lucency of the otocysts it was possible to locate the columnar 

 hematopoetic region mesial to each otocyst. A section through 

 this region (fig. 83) shows the position of these cells ventral to 

 the mesial portion of each otocyst. Traced posteriorly these 

 columns disappear, having absolutely no relation to the inter- 

 mediate cell-mass. The brain tissue is somewhat abnormal. 

 The pharynx and cartilaginous gill-bars are well developed. 

 The abnormal filamentous processes from the pharynx contain 

 numerous darkly staining spherical bodies which when exam- 

 ined at a higher magnification are found to contain small darkly 

 staining globules. These bodies resemble yolk globules some- 

 what in their staining reaction. In abnonnal cases these bodies 

 often become imbedded in the mesenchyme, and might be wrong- 

 ly interpreted as leucocytes or lymphocytes. Ventral aorta and 

 aortic arches are entirely absent. Dorsal aorta is encountered 

 only in a region much posterior to this. 



Figure 84 shows an embryo in which the heart-anlage was de- 

 stroyed before it could be distinguished. At the same time a 

 small portion of the head was isolated. At this time, optic vesi- 

 cles could not be distinguished. An eye developed from the 

 fragment of fore-brain tissue which remained. The otocysts 

 were destroyed. There is no trace of a heart. Erythrocytes 

 developed discontinuously in the intermediate cell-mass. Pro- 



