No. 1.] ORIGIN OF HUMAN MONSTERS. 155 
No. 21. 
Chorion, I2 x 9 x 5 mm.; vesicle within, 5.5 x 3.5 mm. 
From Dr. Cullen, London, Canada, January, 1896. 
The fresh specimen, still inclosed within the decidua, was 
hardened in a large quantity of formalin and sent by express 
in the same fluid. 
Fic, 21a.—Ovum covered with long irregular villi. Slightly enlarged. 
From the external appearance, the ovum is apparently 
normal, with well-developed villi branching a number of 
times. Upon opening the specimen it was found that the 
ceelom is filled with a small quantity of magma reticulé, 
within which is embedded a very large transparent vesicle. 
Fic. 21b.—Interior of chorion, showing magma and vesicle. > 5 times. 
This, with its attachment to the chorion, was removed and 
cut into serial sections 20 microns thick. 
The main vesicle is brought in contact with the chorion by 
means of a small secondary vesicle; both are inclosed with a 
layer of mesoderm within which are numerous blood islands 
