No. 2.] DEVELOPMENT OF THE HUMAN COELOM. 401 
cytogenic studies also. In most of the specimens photographs 
or an additional series of sections were made of the chorion and 
amnion in order to study the variation of these structures. 
Embryos XI,! XII, and II? were completely reconstructed 
in wax by the method of Born. Nos. IX, VI, and X were 
reconstructed in part by Born’s method and finished by His’s 
method of reconstruction. The abdominal viscera of Nos. VI, 
IX, X, XXXIV, XLV, and XLVIII were modeled by Born’s 
method. 
The mechanical portion of reconstruction has been simplified 
to a great extent by a special apparatus used in the Anatomical 
Laboratory,? which enables us to employ a modeler. The sec- 
tions are projected upon a screen, to which the wax plate is 
attached. By working in a dark room with this apparatus it is 
easy to direct a modeler to draw the outlines accurately. He 
can then cut them out, and all that remains to be done is to 
pile the pieces and then blend them. 
THE CoELOM IN YOUNG OVA. 
All of the young human ova which have been described con- 
tain within them a cavity, lined with mesoderm ; this is the 
coelom, bounded by the somatopleure on the outside and by the 
splanchnopleure on the inside. This arrangement, as shown by 
a number of diagrams by recent authors, is very unlike the 
appearance of the blastodermic membranes of many of the 
lower mammals, and it is necessary therefore that we should 
revise our conception of the formation of the amnion in the 
human embryo. 
The ova recently published by Graf Spee indicate that the 
amnion must be formed very early, and, since it is completed 
before the medullary grooves begin, we must admit now that 
it is formed much the same as it is in many rodents, z.e., by 
apparent inversion of the membrane. When Bischoff* first 
described inversion of the membrane in guinea pigs it seemed 
1 Mall: Anatom. Anz. 
2 Mall: Journ. of Morph., vol. V. 
8 Hoen: Johns Hopkins Hospital Bulletin, 1896. 
# Bischoff: Entwickl. d. Meerschweinschens, Giessen, 7852. 
