PLATE 16 



EXPLANATION OF FIGURES 



69 and 70 Are described in detail on page 96. The small arrows indicate the 

 direction of pulsation in the 'accessory heart.' Note the apparently normal 

 condition of the actual heart. 



71 Section through the heart of this same embryo near the plane of section 

 of figure 65. The connection of the fused portions as described in the text is 

 looser than in the plane of figure 65. The right 'arterial' side contains no endo- 

 thelium in this section. Erythrocytes in various phases of development are 

 observed. Note the cul)oidal nature of the endocardium in the left side of the 

 figure. 



72 Section through the heart of the embryo from which figure 55 is made. 

 In this figure the endocardial cells are cuboidal and rather deeply staining. The 

 endocardial cavity contains erythrocytes which are in a column continuous with 

 the erythrocytes of figures 73 and 74. There is a more or less distinct myo- 

 cardium. 



73 Shows a section of the same heart in which a portion of the endocardium 

 and myocardium are transforming into eosinophilous blood-cells. 



74 From the same heart. The plane of section is near the upper end of the 

 heart. The entire endocardium and myocardium of this region has transformed 

 into eosinophilous blood-cells which, as in many instances already noted, are 

 unable to round themselves out for lack of space. 



ABBREVIATIONS 



A.ht., accessory heart Endc, endocardium 



Bl.l., blood lacuna Erth., erythrocytes 



Mijc, myocardium 



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