No. 2.] DEVELOPMENT OF THE HUMAN COELOM. 417 
union of the umbilical vesicle with the body. The reason I 
question von Spee’s interpretation of these small spaces in the 
mesoderm in embryo Gle. is that I believe that all, or certainly 
nearly all, of the body cavity is formed by an incorporation of 
the extra-embryonic coelom within the embryo. What I have 
observed in human embryos as well as in the injected speci- 
mens of Budge shows that this must be true. These small 
spaces in the mesoderm of the body may belong to the muscle 
plates and the early blood-vessels, and certainly cannot play any 
great part in the development of the body cavity. There is no 
doubt whatever that the whole peritoneal cavity is simply 
pinched off from the coelom of the outside of the body and 
it is highly probable that the pericardial cavity and pleural 
cavities are formed in the same way. The anterior mesen- 
tery of the intestine has never existed in the human em- 
bryo, and it is therefore needless to explain its mode of 
disappearance. 
My statements are based in great part on embryos Nos. III 
and XII, and since No. XII is such a perfect specimen it is 
well for me to describe it in greater detail. The embryo is 
about the same age as Kollmann’s! embryo Bulle, which unfor- 
tunately was never fully published. No. III is an embryo 
given me by Professor His. This embryo had been torn from 
the umbilical vesicle, and was injured in different portions of 
the body. Yet the head end of it is fairly well preserved, and 
it is of value in determining the growth of the body walls 
covering the heart. 
Embryo 2.1 mm. long. — The history of embryo No. XII is 
as follows. ‘The woman from whom the ovum was obtained is 
twenty-three years of age and has been married for three years. 
She is avery intelligent woman, and her statements are reliable. 
Her menstrual periods recur every thirty days. She had been 
married some time before she became pregnant, and after pass- 
ing two periods aborted July 6, 1893. She was unwell the 5th of 
October and again on the 7th of November, this last period 
1 Kollman: His’s Archiv, Supplement Bd., 1889, Plate V, Figs. 1 and 2; von 
Lenhossék: His’s Archiv, 1891, Plate I; Kollman: His’s Archiv, 1891, Plate III, 
Fig. 3. 
