Sa ee 
LAMELLIBRANCHIATE CONCHIFERA. 93 
distributed to the mantle the calcareous matter to the valves, which in a more perfect 
animal is only got rid of, by being secreted by a glandular organ, and thrown out by an 
excretory orifice. In higher Mollusca, for instance, we find the coloured secretion in 
some furnished by the veins of the mantle, in others accumulated into a glandular bag. 
Swammerdam believed the dark-coloured organs of the Lamellibranchiata to be con- 
cerned in the formation of the shell, as did Poli, who terms them the testaceous viscera. 
De Blainville compares them to kidneys ; and I think I have said much to confirm his 
opinion. 
An analogous condition may be observed in the Radiata. In the Stellerides the veins 
of the viscera meet, and become conjoined with a brownish spongy substance, forming 
two organs, which probably open without, through the dorsal plate or disk, or near to it. 
From this disk there extends, by the side of the spongy substance into the circular 
union of the hydroferous canals, a cylindrical calcareous part, which is articulated, 
and appears to be analogous to the stem of the Pentacrinus, but which has become 
internal by the formation of the dorsal integument. The naked Acephala being desti- 
tute of calcareous parts, have scarcely a rudiment of secreting organs ; but in the Gas- 
teropoda a secreting organ always exists when there is a shell. This organ is evidently 
formed in them by a tissue of veins. In the Patella it opens by the oviduct and rectum, 
and is situated over the viscera: de Blainville considers it to be the organ of respiration 
in these animals. In some Patelliform animals there are two orifices. The orifices in the 
Chiton are between the branchial processes, not far from the oviducts. Where there is 
no trace of a shell, secreting organs are not present. In the species of Doris, which 
have commonly calcareous matter in the integument of the back, the sac described by 
Cuvier as opening near the anus seems a rudiment. In Bullea aperta, which has a 
shell, two glands exist by the mouth, though overlooked by Cuvier. It is needless to 
mention that an organ secreting mucus and calcareous matter is found in all spiral 
Gasteropoda. It (the mucous sac of authors) sometimes opens near the anus by a duct, 
as in the Phytivora; or by a large opening at the back of the branchial cavity, as in 
the Carnivora ; in which latter case the animal probably has the power of breathing air 
by means of it when out of the water. 
The mucous sacs of the Cephalopoda, opening by papille on each side the rectum, are 
traversed by the great veins which secrete into them, from particular appendages on 
their surface, much muco-calcareous matter. The bile ducts, likewise, pass through 
the cavity, and secrete into it. In these animals, the blood from the visceral veins 
seems directed into the hepatic, as was noticed by Cuvier; and I consider their circu- 
lation to be intermediate to that in which the ovarian, intestinal, &c. blood goes to the 
liver, and that in which the hepatic, intestinal, and ovarian blood all passes through 
the excretory organ. No molluscous animal appears to possess absorbents, hence the 
necessity of the skeleton being external and out of the circulation. 
