COMMUNICATION OF VASCULAR SYSTEM. 
429 
On the Supposed Communication of the Vascular 
System with the Exterior in Pleurobranchus. 
By 
Alfred Gibbs Bourne, D.Sc. Loud.. F.L.S., 
Assistant Professor of Zoology and Comparative Anatomy in University 
College, London. 
With Plate XXIX. 
Lacaze-Duthiers 1 has described in Pleurobranchus a 
special canal opening on the one hand to the exterior and on 
the other to the branchial vein, and in Dentalium, two 
orifices leading from the exterior into the two great veins in 
the mantle. 
These statements have remained hitherto unchallenged. I 
have not examined Dentalium in this respect, but in the 
case of Pleurobranchus I am in a position to deny the exist- 
ence of any such communication. 
At the request of Professor Lankester, who had long desired 
to re-examine the structure described by Lacaze-Duthiers in 
Pleurobranchus, I prepared some specimens of this mollusc 
when at Naples in the spring of last year, and I have recently, 
at Professor Lankester’s request, completed the examination of 
this material in the laboratory of University College. 
The orifice described by Lacaze-Duthiers in Pleurobran- 
chus may be easily found (PL XXIX, fig. 1, x), but further 
1 Lacaze-Duthiers, ‘Ann. Sci. Nat.,’ ser. 4, vol. vi (Dentalium), and 
1. c., vol. xi (Pleurobranchus). 
