ANATOMY OF THE LAMELLIBRANOHIATA. 295 



the appearance, at certain times, of a greyish matter diffused 

 over the whole body, and entering into all the tissues. We 

 know that the shell is more enlarged at some periods than at 

 others, and this accumulation may precede the deposition, as 

 a provision for its accomplishment ; or it may be for the pur- 

 pose of being thrown off by the excretory organs, as it is in 

 the veins which surround them that the accumulation princi- 

 pally takes place. The grey matter is certainly composed of 

 carbonate of lime. 



The excretory organs throw off mucus and colouring mat- 

 ter, as well as carbonate of lime. The latter is often found 

 within them in concretions of a crystalline appearance, and 

 of an orange, pink, or purple colour. The situation of these 

 organs has been described above. In all molluscous animals 

 they are between the branchiae and veins returning from the 

 body. In the Pecten, a minute orifice leads directly on each 

 side into them. The oviducts likewise enter them. Above 

 each excretory sac leads into a single transverse cavity under 

 the pericardium. In the Unio &c, an orifice, close to that 

 of the oviduct, leads into a large cavity of the mantle, under 

 the pericardium, into which the secreting organ opens by an 

 internal orifice. Boj anus was not aware of this internal open- 

 ing, or he probably would not have considered these organs 

 to be lungs. The external orifice is seen to open at the an- 

 terior angle formed by the foot and the branchice. The ovi- 

 duct is also distinct from the sac in Modiola, Mytilus, Litho- 

 domus, &c, whilst in Tellina, Cardium, Mactra, Pholas, 

 Mya, and most others, the ova are discharged into the secret- 

 ing organs. Generally the secreting orifice is near the pos- 

 terior muscle, and the oviduct more anterior. The former is 

 often minute and difficult to find, and in the oyster it is ab- 

 sent altogether, and there is little trace of the excretory or- 

 gans themselves : here we may conclude, from the great 

 quantity of calcareous matter thrown off to the internal part 

 of the valves, that the vessels have not become perfected into 

 a gland, but, as is common in higher Mollusca, throw off from 

 their extremities distributed to the mantle, the excretions, 

 which, in a more perfect organization, are only got rid off by 

 being secreted by a glandular organ, and thrown out by an 

 excreting orifice. Swammerdam 1 considered these organs to 

 be concerned in the formation of the shell, as did Poli, who 

 terms them " the testaceous viscera.'''' Blainville, in his re- 

 marks on the opinions of Boj anus regarding them, compares 

 them to kidneys ; and the author thinks he has said much to 



1 BiWia Naturae. 



