1888.] between the Body-canty and the Vascular System. 219 
by connective tissue, and between two of the longitudinal vessels; 
it contains usually only blood corpuscles, which are exactly like 
those found freely in the body-cavity; but in individuals which 
are sexually ripe, spermatozoa and ova are often found in it. The 
openings, by means of which the cavity of this vessel communi- 
cates with the coelom, can be seen if the vessel be dissected out 
and exposed under a microscope; and further, Vogt and Yung" 
state that it is easy to inject the former from the latter. 
Another group which stands far apart from both the Hirudinea 
and the Gephyrea, and in which communications exist between 
the vascular system and the ccelom, or at any rate with part of 
it, is the Echinodermata. Here, according to the observations of 
Hamann and Koehler, in Spatangids at least the blood system 
is in communication with the water vascular system, embryo- 
logically a part of the coelom and developed from an outgrowth 
of the body-cavity. And according to the French school of 
naturalists who have worked at this group, and amongst whom 
Perrier is the most prominent, this connection may be extended 
to the whole group of the Echinodermata. 
Finally, in the class Vertebrata we again find the body-cavity, 
which is admittedly coelomic in nature, in communication with 
the vascular system, which is to some extent at any rate archi- 
coelomic. The means of communication is through the lymphatic 
system. This opens on the one hand into the body-cavity by 
means of open stomata, and on the other by means of the thoracic 
duct into the venous system. 
That fluids can pass from the body-cavity into the blood system 
by means of the lymphatic system has been shewn both by 
Recklingshausen and by Ludwig. The former found that milk 
put upon the peritoneal surface of the central tendon of the 
diaphragm—where numerous stomata exist—shewed little eddies 
caused by the milk globules passing through the stomata and 
entering the lymphatics. Ludwig’s experiment is even more con- 
clusive. He took a dead rabbit, and removed its viscera, and placed 
it so that the peritoneal surface of the diaphragm was exposed. 
He then poured into this a solution of Prussian blue, and, after 
imitating the respiratory movements for a few minutes, he ob- 
tained the lymphatics filled with a blue injection, shewing a 
beautiful plexus. 
A more direct communication between the blood system and 
part of the body-cavity has been described in one Vertebrate. 
Weldon’ has described and figured the structure of the head 
1 Vogt and Yung, ‘‘ Lehrbuch der Praktischen Vergleichenden Anatomie.” 
2 “On the Head Kidney of Bdellostoma,” by W. F.R. Weldon. Q. J. M.S. 
Vol. 24, 1884. 
VOL. VI. PT. IV. 16 
