64 



H. VON W. SCHULTE 



nants of the partitions separating its component angiocysts. 

 On the left but one minute one is present. The separated 

 lumina at the shoulder of the left ventricle are due to collapse 

 of the tube. Between the two ventricles is a net work of mesen- 

 chyme strands which have for the most part a longitudinal direc- 

 tion. In the model of the lumina but two angiocysts arejound 

 in this area, one median in position, one close to the leffendo- 



Fig. 10 Lumina of endothelial tubes of eml)ryo shown in figure 9, same scale. 

 1, Bulb; 2, isthmus; 3, ventricle; 4, omphalo-mesenteric vein; 5, atrio-venous 

 angle; 6, angiocysts. 



thelial tube. The irregular contours of both tubes mesad sug- 

 gest the addition of imperfectly assimilated angiocysts. 



In embryos of 12 and 13 somites the mesenchyme of the middle 

 cardiac plate is condensed into a single strand which occupies 

 the concavity of the plate between the ridges which demarcate 

 it from the mantles (figs. 11 and 12). In the model of the en- 

 dothelium (not illustrated) this strand extends from the con- 

 stricted regions or isthmi between bulbs and ventricles as far as 



