416 MALL. [Vot. XII. 
embryo, that is, the cavity of the muscle plates, pericardial 
cavity or peritoneal cavity. It is impossible to determine defi- 
nitely which portion of the body cavity these spaces represent, 
but I do not feel inclined to believe that what he marks peri- 
cardial cavity in Fig. 23 can possibly represent it, for we are 
to look for the pericardial cavity between the junction of the 
pharynx and umbilical vesicle and the head end of the embryo. 
This portion of the embryo is marked H in my Fig. 15, and 
falls ‘anterior to.von’ Spee 's Hig. 16. Ven Spees Figs 16us 
the 24th section of the embryo, beginning at the head, while 
his Fig. 23 is the 81st section. 
The various small spaces in different portions of the meso- 
derm cannot be viewed as the real origin of the body cavities 
without further discussion. In the von Spee embryo v. H. there 
are indications already of small spaces in the mesoderm at the 
border of the ectoderm of the embryo. Similar spaces are 
described by Bonnet? for the sheep and by Selenka? for the 
monkey. While von Spee and Bonnet believe that these 
spaces belong to the coelom, Selenka simply designates them 
heart, or vascular. 
The blood-vessels are intimately associated with the coelom 
in their early development, and it is easy to be led into error 
without an abundance of material. Drasch® recently has 
again emphasized this relation. He has shown in the chick 
that the blood islands are separated from one another by a 
number of closed spaces filled only with a fluid. These spaces 
soon flow together to form the large slit-like coelom of birds. 
The same condition of things has been shown to be true, but 
from a very different method, by Budge. He injected the 
blastoderm of the chick, and showed that the coelom was com- 
posed of a network of spaces, which gradually flowed together 
into the large coelom surrounding the embryo. 
Of course in the young human embryos we have at our dis- 
posal this stage of the process has long passed, but there is no 
reason why a remnant of it should not exist at the point of 
1 Bonnet: His’s Archiv, 1889. 
2 Selenka: Studien, etc., Taf. XX XVIII, Fig. 35. 
8 Drasch: Anatom. Anz., Bd. 9. 
* Budge: His’s Archiv, 1887. 
