NOTES ON THE HISTEIOBDELLIDiE. 
201 
vessel, and it often happens that under such circumstances 
none are to be found in the branchial chambers. 
Body-cavity. 
Surrounding the enteric canal, between the wall of the 
latter and the wall of the body, is a space of considerable 
size, which occupies the position of the coelomic cavity of the 
Annulata. This is referred to by Focttinger (3, p. 490) as the 
cavite generale du corps,^’ and is described by him as a 
cavity between the musculo-cutaneous tube and the digestive — 
bounded by somatopleure and splanchnopleure, which are 
stated to be thin cellular membranes with flattened nuclei. 
A corresponding cavity in the head is said to be completely 
cut off from the body cavity of the trunk by a septum 
composed of large cells. The somatopleure of the trunk is 
described as clothing the dorsal and ventral muscles and the 
nerve-cord. 
Shearer ( 9 ) terms the cavity in question blastocoelic cavity 
on the assumption that it corresponds developmentally with 
the similarly situated cavity in Dinophilus, and that the 
latter is of blastocoelic derivation. He describes prolonga- 
tions into the head and into the posterior limbs. He doubts 
the correctness of the view that it is lined by a coelomic 
epithelium. 
The gut surface, he admits, is lined by a delicate cuticle^’ 
with small flat nuclei at rare intervals, and he maintains that it 
is difficult to say if this is a membrane or a “ mere secretion 
from the blastocoelic ends of the cells of the gut-wall.’^ The 
somatopleural side of the cavity, he asserts definitely, is not 
lined by any such membrane : the longitudinal muscles, as in 
Stratiodrilus, are surrounded by a delicate cuticle similar 
to that which lines the outside of the gut, but no nuclei are 
to be seen in it. He maintains that neither the splanchnic 
nor the somatic layer is of the character of a true peritoneal 
or coelomic epithelium. 
I have not yet been able to work out definitely the 
