358 MALL. [Vor. XIX. 
throughout the blood in the tube and in many instances are 
attached to the decidua. The syncytium is well developed. 
The walls of the tube are markedly distended, infiltrated with 
red corpuscles and leucocytes, many contain fragmented nuclei, 
which are also scattered throughout the decidua. 
Within the ccelom of the chorion there is a double vesicle, 
the large one, 2 x I mm. in diameter, showing all the char- 
acteristics of the umbilical vesicle. Its layer of mesoderm 
appears to be thickened and at numerous points it has become 
adherent to the inner wall of the chorion. At these points 
the blood islands extend over to the mesoderm and from them 
blood-vessels ramify to all of the villi. These vessels are all 
filled with nucleated blood cells. The smaller vesicle is about 
a millimeter in diameter, is lined with cylindrical cells and is 
covered with quite an even layer of mesoderm, in which there 
are some quite large blood-vessels but no blood. Towards 
one of its ends it is covered with a marked layer of cylindrical 
cells. It may be that this second vesicle represents what is 
left of the embryo. Around these two vesicles, filling the 
whole ccelom, there is a dense reticular magma. 
The main wall of the chorion and many of the villi are 
somewhat fibrous in structure. Some of the villi are being 
invaded by syncytial cells. 
This specimen is especially valuable inasmuch as it shows 
the early changes which take place in an ovum after it became 
lodged in the uterine tube. No doubt owing to its faulty 
implantation the nutrition of the embryo was affected and 
it consequently grew in an irregular fashion. The umbilical 
vesicle became adherent to the chorion and its blood-vessels 
grew out into most of the villi. 
No. 398. 
Embryo, 5 mm. long. 
Professor C. R. Bardeen, Madison, Wis. 
The embryo is markedly changed and of the three-weeks’ 
stage. Most of the organs can still be recognized and the 
embryonic ccelom is fairly definite. The front of the head is 
