COMMUNICATION OP VASCULAR SYSTEM. 
431 
Opisthobranchs to which Pleurobranchus belongs? Is 
it nephridial in nature ? If it were it would be the rudiment 
of the second nephridium which persists in so few Gastropods 
(e . g . Fissurella, Patella) since there is a nephridium as 
well developed in Pleurobranchus as in Aplysia. This 
is not likely ; its structure is not nephridial and I am con- 
vinced that it has no opening into the pericardium. Professor 
Lankester has suggested to me, and the view seems an extremely 
probable one, that we have here the homologue of that grape- 
shaped gland in Aplysia which has been long known as the 
“ poison-gland." The position of the orifice of this gland is 
shown in fig. 2, z, and corresponds precisely in position with 
that of my sac. 
Whether this suggestion as to the homology of the organ 
prove correct or not, it is I think quite certain that the special 
means of communication between the vascular 
system and the exterior, which has always been 
stated to exist in Pleurobranchus, has no existence. 
