464 



MISS K. M. PARKER ON THE 



cavity extending round the embryo and with the lateral limbs 

 prolonged into the somitic region. The endothelial primordia of 

 the heart are represented by more or less continuous tubes, solid 

 cords, and scattered angioblast cells difierentiating in the postero- 

 anterior direction and lying between the entoderm and the 

 splanchnic mesoderm. 



The endothelial heart-tubes are the only vessels yet established. 



Text-figure 4. 



^^i?iv'*AVrV-"- 



% 



H % 



i\ 



Dasi/urtis viverrinus (V'o mm. vesicle). Longitudinal section, median 

 through the anterior margin of the brain-plate. 



^m«. Head-fold of amnion. JEwi. Entoderm. P.p.C. Pleuro-pericardial canaL 

 T.B. Terminal ridge. 



Stage II. Dasyurtis viverrimi^s (8*5 mm.). 



The material for this stage consists of one embryo (A) of 

 Dasyurits viverrinus cut transversely and one (Aa) cut longi- 

 tudinally. A graphic reconstruction of the gut and pericardium 

 together with the endothelial heart-tube and aorta of the left 

 side of embryo A will be found in PI, I. fig. 3. 



