A Human Embryo with Seven Pairs of Somites. 95 
A survey of the literature gives very limited information on the 
primitive vascular development. ‘The first suggestion of a vascular 
anlage is a very indistinct knotty appearance in Peters’ embryo; 
Keibel, however, who made a reconstruction of this ovum, says this 
appearance is merely suggestive and that no positive conclusions 
can be drawn. None of the several other young ova show any vas- 
cular formation. Embryo Frassi 1.17 mm. shows the first blood 
vessels, which are distributed in the chorion, bauchstiel and ventral 
pole of the yolk sac. No vessels were observed in the body of the 
embryo. Graf Spee’s Gle 1.54 mm. is probably next in point of age, 
followed very closely by Eternod’s 1.3 mm. embryo. Graf Spee 
describes the first anlage of the heart, otherwise there are no vessels 
in the body of the embryo; blood islands are present in the ventral 
pole of the yolk sac, but no mention is made of vessels in the bauch- 
stiel or chorion. Eternod’s 1.3 mm. embryo is the first specimen to 
present a complete circulation. It has a very well developed umbil- 
ical circulation and the villi are partly vascularized, but no vitel- 
line vessels could be detected. The Kroemer-Pfannenstiel embryo 
Klb. of approximately the same age as the embryo under considera- 
tion is said to have a very large umbilical artery, unaccompanied 
however by a corresponding vein, also omphalomesenteric veins are 
present but no corresponding arteries. ‘The vessels in the yolk sac are 
full of corpuscles, but no mention is made of any chorionic vessels. 
This summary of the earliest vascular development is by no means 
evidence in favor of a primitive vitelline circulation. Although the 
facts are very meager on account of the scarcity of material and 
nothing positive can be deduced, nevertheless there seems to be some 
evidence in support of a primitive umbilical circulation. The first 
embryo having a complete circulation is Eternod’s (1.3 mm.), with 
a well developed umbilical circulation. From the other remaining 
specimen (Kroemer-Pfannestiel Klb.) between Eternod’s and our 
embryo it would be hard to draw definite conclusions on account of 
the presence of the artery of one system and the vein of another, 
forming no complete circulation.— 
The presence of capillaries in the chorion, bauchstiel and yolk sac 
in Embryo Frassi would seem to indicate that the mesoderm which 
forms all of the above structures, is endowed with a high power of 
