Mr. W. Clark on the Animal of Kellia rubra. 453 
pure fluid is expelled by the aperture of ingress, a small portion, 
as before stated, passing out by the posterior siphonal apparatus. 
In this case the apertures of gress and egress are not “kept 
distinct.” 
In those mollusca with nearly closed mantles only a small por- 
tion of fluid can enter by the restricted pedal orifices; the far 
greater part must be inhaled by the posterior siphons, and is 
often expelled simultaneously at both orifices, as I have observed 
in Pholadidea papyracea, the most closed of all the bivalves; and 
whether the water be received through the anal or branchial 
tube, or both, the fact of the simultaneous expulsion of the fluid 
in almost equal streams proves that the known branchial cco. 
nomy of the bivalves does not require the apertures of inhalation 
and exhalation “to be kept distinct,” as it is clear that water is 
expelled by one at least of the tubes of ingress. 
The doctrine of the known ceconomy of the bivalves, requiring 
the apertures of ingress and egress to be kept distinct, cannot, I 
think, be admitted; it has not been verified by competent 
authority. I do not believe in it, as it is disproved by indis- 
putable facts. 
_ I have little doubt that the water required for buccal and 
branchial uses, in the mollusca with closed mantles, is received 
through both the posterior apertures, anal and branchial as they 
are called; and probably at their bases there is an internal com- 
munication, thus allowing the water from both to pass into the 
great cavity of the branchiz, to bathe them, and for sustentation 
of the animal; and after these functions are fulfilled, it is in like 
manner expelled from hoth orifices, and often simultaneously, as 
may be seen in any of the Pholades, Lutrarie, or Mye. 
The water, I believe, never makes a circuit, or enters the legi- 
timate anal tube, or issues therefrom, and which, to prevent con- 
fusion, ought to be denominated the rectum, or that portion of 
the viscera proceeding from the stomach to its termination at 
the posterior end of the body, where it empties itself into a con- 
duit termed the anal tube. The legitimate anal cylinder, or 
rectum, is only for the discharge of the rejectamenta of the ali- 
ment entering the buccal orifice, and from thence passing to the 
stomach ; for if the water entered this duct, either posteally or 
anteally, in the one case it would force back the feces into the 
stomach, and in the other none would ever be found in the rec- 
tum ; but the scalpel shows it is always filled from its point of 
junction with the stomach to its terminus with a cylindrical com- 
pact mass of feecal matters, which, as the animal requires, is dis- 
charged by minute portions into the anal conduit; the water 
therefore for the branchiz and sustentation must pass into the 
great branchial cavity, and issue therefrom by both the ducts at 
