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It is now maintained by those who hold that the former pheno- 
menon does in some way occur — that the channel by which the blood- 
fluid makes its escape is from the pericardium through the reno-peri- 
cardial pores. A fact of fundamental importance is assumed in this 
view, namely that the pericardium of Molluscs is part of the general 
vascular system and contains blood. I have satisfied myself that this is 
not the case in Solen legumen. According to the observations of Pen- 
rose (Brit. Assoc. Reports 1882) and more recently of Bourne the peri- 
cardium of that Lamellibranch never contains the red-coloured blood, 
but it is occupied by a colourless fluid. 
The current statements that in Anodon the pericardium communi- 
cates with the blood-vascular spaces by means of veins — also appear 
to me to be erroneous. I can not admit, after careful examination of 
the pericardium of Anodon by means of silver-staining, and other me- 
thods, that there are any veins opening into it. 
On the whole it appears to me that there is no sufficient evidence 
that the pericardium of Molluscs is in any case (except perhaps the 
Neomeniae) a blood-space. Accordingly the blood can not escape 
through it and the renal organs to the exterior. 
3) As to the introduction of water into the vascular system by 
pores in the foot, now maintained especially by Griesbach, there is, 
as in the case of the supposed out-shedding of the blood, not only a 
want of evidence that the process takes place at all, but also a want of 
evidence that the pores by which it is supposed to be effected have 
any existence. Five years ago I examined very carefully complete 
series of transverse sections through the foot of Anodon and of Solen 
and could find no such pores as have from time to time been described, 
nor any break in the epithelial clothing of the foot which could serve 
as an entrance to the sub-epithelial vascular spaces. 
If Dr. Griesbach desires to establish his statements as to the 
admission of water into the vascular system of Lamellibranchs by pores 
in the foot, he must shew fully and clearly ina manner convinc- 
ing to the histologist that such pores exist. He has done no- 
thing in this direction at present which can be regarded as tending even 
in a small degree to prove that there is any reality in his suppositions. 
Also he must bring better evidence of the entrance of fluid by pores 
into the vascular spaces of the foot, than is afforded by the diffusion of 
a soluble colouring matter. He has found that finely divided coloured 
powder can not be made to enter the vascular system through the sur- 
face of the foot. Until he can shew either that such powdered colour- 
ing matter can enter or that there are demonstrable pores on the foot 
leading to the vascular system, it seems to be unreasonable in the face 
