CIRCULATION IN MOLLUSCA. 219 



where the blood effused into the visceral cavity, is in con- 

 tact with and, as it were, bathes the alimentary canal, there 

 may be a transference of chyle from it directly into the 

 blood, and a similar transference of the aqueous portion of 

 this into the intestine, — an exchange regulated by the well- 

 known law of endosmose, — yet I cannot but think that many 

 doubts may dwell reasonably over this part of their physi- 

 ology. 



You will observe that the reservoirs or lacunas hitherto 

 mentioned, which interrupt the circulation, receive only 

 venous blood, but in the Haliotis and Patella, this degrada- 

 tion in structure reaches the arterial system also. In them, 

 and in the genera allied to them, the aorta having reached 

 the point at which the digestive canal is bent back, on the 

 superior aspect of the pharynx, to descend into the abdo- 

 minal cavity, opens direct into a vast cavity or lacuna con- 

 taining the fleshy mass of the mouth, the salivary glands, 

 and the cerebral ganglia, which are consequently surrounded 

 by and bathed with the arterial blood. From this reservoir 

 the blood is afterwards sent to the foot and to the appen- 

 dages of the head. What is still more singular, the aorta 

 in these animals fulfils functions analogous to those of the 

 abdominal cavity, for, in the Haliotis, it actually contains 

 within its tube the superior portion of the digestive organs ; 

 and, in the Patella, the membranous sheath of the base of 

 the tongue receives the arterial blood ; and from it the 

 whole of the arterial system can be injected. M. de Qua- 

 trefages asserts, that he has found a similar deficiency of the 

 arterial system in some species of Eolidas. 



These views of Milne-Edwards have been confirmed to a 

 greater or less extent by Valenciennes, Owen, E. Blanchard, 

 Nordman, M. de Quatrefages, and others, and must be re- 

 ceived as in general correct. The accuracy of their full 

 application to the Nudibranchia has been questioned by two 

 most competent anatomists, Messrs. Hancock and Emble- 

 ton. We shall have a future opportunity of mentioning 

 some views relating to the circulation in this tribe, by M. de 



Edwards et Valenciennes. Ibid. p. 307. — Lettre sur l'Appareil de la 

 Circulation chez les Mollusques de la Classe des Brachiopodes ; adressee a 

 M. Milne-Edwards par M. R. Owen. Ibid. p. 315. — De l'Apparcil circula- 

 toire du Poulpe, par M. Milne-Edwards, ibid. p. 341. — Me'moire sur la 

 Degradation des Organes de la Circulation chez les Patelles et les Halio- 

 tides, par M. Milne-Edwards. — Ibid. viii. (1847), p. 37. De l'Apparcil 

 circulatoire du Calmar. — Ibid., p. 53. — De l'Appareil circulatoire de 

 PAplysie, Ibid. p. 59. Dc l'Appareil circulatoire des Thethys, Ibid. p. 

 64. — De l'Apparcil circulatoire du Colimacon, p. 71. — Systemc circulatoire 

 du Triton, Ibid. p. 75. — Dc l'Appareil circulatoire de la Pinine marine, 

 Ibid. p. 77. 



