No. 2.] DEVELOPMENT OF THE HUMAN COELOM. 423 
embryo XII, as well as in Kollman’s embryo Bulle, indicate 
that the first plates must belong to the occipital region, and I 
have found that there are three occipital muscle plates in 
embryo No. II.! Moreover, there is every indication of a 
degeneration of the first two plates in XII, so on this account 
I am inclined to number them as they are numbered in Fig. 
16. Ido not think that any of them ever communicate with 
the pericardial cavity as Bonnet found them in the sheep. The 
cavities in all of the other plates are small, and they are sep- 
arated by a large mass of mesoderm from the coelom. This 
all confirms my view. 
The chorda extends from Seessel’s pocket to the neurenteric 
canal. 
There are also a few segmental ducts, some completely and 
some partly separated from the ectoderm, as was the case in 
Kollman’s embryo. The ducts are small, and extend over one 
or two sections only, and occasionally one of them is arising at 
several different points between a given two segments. They 
are present on both sides between the first and second cervical 
segments, second and third segments, third and fourth segments, 
fourth and fifth segments, and only on the left side in the region 
of the fifth and sixth cervical segments. 
The coelom of this embryo is especially instructive. A 
sagittal section of the embryo and ovum is given in Fig. 21. 
This embryo, when drawn connected with the ovum, is very 
similar to Graf Spee’s embryo Gle. as shown in Fig. 15. It is 
very easy for us to conceive the von Spee embryo converted 
into this embryo, for about all the change that is necessary is 
that the embryo grow somewhat and bend upon itself. In so 
doing the attachment of the umbilical vesicle becomes smaller 
as the amnion encircles the body of the embryo more. The 
position of the neurenteric canal, the shape of the allantois, 
and the formation of the pericardial cavity, all show that the 
curving must be a normal one. 
Nearly all other young embryos of this stage, or a little older, 
which have been published show a straighter body or even a 
curve in the opposite direction. I have also in my collection 
1 See also Mall: Journ. of Morph., vol. V. 
