296 ANATOMY OF TPIE LAMELLIBRANCHIATA. 



confirm this opinion; and that what happens in the higher 

 animals with regard to the liver, as to its circulation, takes 

 place here in these organs. l 



An intimate acquaintance with the anatomy of the Radiata 

 and Mollusca, will show that where there is a shell secreted, 

 some part of the venous system goes to form a spongy organ 

 or pair of organs, which communicate with the exterior, and 

 secrete a calcareous matter, when the system is not unloaded 

 at the periods of the formation of the shell. Thus, in the 

 Stellerides, below the calcareous disk, noticed on the dorsal 

 surface, the veins of the viscera meet, and become conjoined 

 with a brownish spongy substance, forming two organs which 

 probably open without, through this disk or plate, and com- 

 municate on the other hand with certain canals in which the 

 water circulates. 2 The Tunicata, having but a trace of cal- 

 careous parts, as has been described above, have only a ru- 

 diment of the secreting organs. In the Gasteropoda, a se- 

 creting organ always exists when there is a shell. Tt has 

 two systems of veins, — branches sent from the visceral 

 veins, the ramifications of which form its tissue, — and others 

 which enter the auricle from it. In the Patella it opens by 

 the oviduct and rectum, and is situated over the viscera ; 

 Blainville considers it to be the organ of respiration in these 

 animals ; it is here single. There are two in the Chiton ; 

 their orifices are between the branchial processes, not far from 

 the openings of the oviducts. In Eolida and Tritonia, na- 

 ked genera destitute of a shell, the author does not find them. 

 In the Doris there is a sac, as is described by Cuvier, open- 

 ing near the anus, which is probably the organ of secretion ; 

 and in some species of this animal, it may be seen that there 

 is much calcareous matter in the dorsal tegument. In Bul- 

 Icea aperta there is a small shell, and also, though unnoticed 

 by Cuvier, two small glands, situated on each side the mouth, 

 of a greenish colour ; their situation is perhaps so, from the 

 disposition of these organs to connect themselves with the 

 generative outlets, which, in part, are situated in this animal 



1 Uric acid has been found in the excretory organ of the Gasteropoda, 

 Jacobson, 'Journ. de Phys.' t 91 ; and in those of the Lamellibranchiata, 

 Treviranus, Zeitschrift, &c. 



2 From this disk extends likewise, by the side of the dark spongy sub- 

 stance, into the circular union of the canals, which run in the centre of the 

 radiated rows of articulated pieces, a cylindrical calcareous part, itself arti- 

 culated. The author considers this part to be analogous to the stem of the 

 Pentacrinus, but become internal by the formation of the dorsal integu- 

 ment. The disk appears to be the base of the pedicle, fixed in Pentacrinus . 

 The canals are analogous to those for which we see the perforations in the 

 fossil remains. 



