299 
and other matters relating to the spectroscope, will be brought 
forward soon elsewhere. 
The dorsal vessel in Oligochceta . — The relation of the vas- 
cular system in these worms is, very clearly, primarily to the 
alimentary canal ; the cutaneous vascular system is an addi- 
tional development. In many cases the contractions of the 
dorsal vessel contract the intestine simultaneously, and the 
same movement acts most obviously on the perivisceral fluid, 
expansion of the vessel acting so as to contract the peri- 
visceral cavity. A similar action is well seen in some Crus- 
tacea (e. g., Branchipus) ; the fluid in the lacunae surrounding 
the dorsal vessel moves in one direction rhythmically with the 
movements of the vessel. The corpuscles of the perivisceral 
cavity are, in jDligochaeta, mainly , but not entirely, derived 
from the coarsely cellular membrane, which surrounds the 
dorsal vessel and its branches, and which has been called the 
hepatic tunic. The corpuscles of the perivisceral fluid 
furnish good specific, and even generic, characters among 
Oligochaet worms. "We have here a good case of the value 
of “ cell-diagnosis.” 
VOL. IX. —NEW SEK. 
u 
