70 MALL. [VoL. XIX. 
itself felt at the very apex of the growth, and in the early 
stages of development this is in the amnion, including also 
the ectodermal plate. 
At this early stage, probably during the second week of 
pregnancy, the three primary layers have established them- 
selves well in their capsule of decidua, which must give nour- 
ishment to all sides of the ovum through the syncytium and 
young villi. In looking through sections of young ova one 
cannot help but think that the syncytial cells form the aggres- 
sive elements which eat themselves through everything that 
comes before them and cause the mucosa of the uterus to 
respond at once. Hemorrhages naturally follow such an 
action, and, judging by the frequency free blood is found 
between the villi, it appears that in all cases the blood comes 
in direct contact with the syncytium, which then grows so 
much the better. This vigorous layer of cells no doubt nour- 
ishes the layer of mesodern below it, which in turn cares for 
the embryo, for at this time there is no vascular system to 
carry the food from the mother’s blood to the embryonic disc. 
The villi which are growing so rapidly must cast some of the 
fluid within their mesenchyme into that of the main wall of 
the chorion as it splits into two layers to form the ccelom. 
Thus, for a time, even after the blood-vessels are formed in 
the umbilical vesicle, the nutrition of the embryo passes 
through the ccelom exclusively. The first blood-vessels to the 
embryo hasten the process from the umbilical vesicle, and it 
is not until the heart is formed and the vascular system has 
reached the villi that the nutrition passes in through the 
umbilical cord. This does not take place until the embryo is 
fully 1.5 mm. long, 7 e., in the specimens of Eternod and 
Graf Spee. From now on the amnion begins to expand, at 
first very slowly and later much more rapidly, and gradually 
obliterates the exoccelom. This is complete by the time the 
ovum is 45 mm. in diameter and the embryo is 20 mm. long. 
About the time the blood-vessels are formed and reach the 
embryo an interference in the nutrition of the embryonic mass 
naturally results in the destruction of the anlage of the 
