Vascular System of Bdellostoma dombeyt. 35 
the posterior lobe and breaks up into capillaries in the tissue 
of the liver. 
I have observed in several cases a marked terdency fcr the 
injected carmine gelatine to escape from the blood vessels 
into the surrounding lymphatics, which are very numerous 
and extensive. These lymphatic spaces, especially the sub- 
dermal spaces in the caudal region, and the peri-branchial 
spaces around the gill pouches, are usually found more or less 
injected, although the blood vessels show no signs of over- 
distension. The lymphatic spaces around the vessels in the 
gill itself are also often filled. This condition may be inter- 
preted as indicating that the capillary walls are unusually 
weak and permeable, so that the injected liquid passes 
through them, carrying blood corpuscles with it. That this 
process is not normal is shown by the absence of red blood 
corpuscles from these lymphatic spaces in life, and in unin- 
jected specimens. 
REMARKS ON COMPARATIVE ANATOMY OF BDELLOSTOMA. 
The communication of the pericardial cavity with the peri- 
toneal cavity through the pericardo-peritoneal foramen is 
primitive. The heart, which is a specialized portion of the 
primitive sub- intestinal vessel, always develops at first in 
the anterior end of the general peritoneal cavity. In all 
adults, however, a special pericardial cavity is formed. In 
Petromyzon, whose pericardial sac is enclosed in a cartila- 
ginous pocket, the separation is complete. In the larval 
Ammoccetes, however, there exist two larval pericardio-peri- 
toneal foramina, one on either side. Communication between 
pericardial and peritoneal cavities exists also in Elasmo- 
branchs and Ganoids, but only during embryonic life in all 
higher vertebrates. 
Although its embryological development is not yet worked 
out, the sinus venosus doubtless at first receives a right and 
left ductus Cuviert, like Petromyzon (Goette), and higher 
forms. ‘The right ductus has probably been lost altogether 
in a manner which will be discussed later. The left ductus 
Cuvieri has apparently fused with the sinus venosus, and is 
represented by the external portion of the posterior expanded 
23 
