Natural History of Molluscous Animals. 



91 



Art. VI. An Introduction to the Natural History of Molluscous 

 Animals. In a Series of Letters. By G. J. 



Letter 9. On their Circulating System, 



Sir, 



Aristotle divides animals into those which have blood, 

 and those which have none ; and these primary classes were 

 appropriately named the sanguineous and exsanguineous. 

 Among the latter he places the Mollusca, as all naturalists 

 did for a long time afterwards, and as all, except naturalists, 

 continue to do. Blood is scarcely known to the vulgar unless 

 by its red colour ; and so essential is this character deemed, 

 that it appears to them little less than an abuse of language 

 to apply the term to any white or colourless fluid. Even 

 Linnaeus seems to have participated of this prejudice, and to 

 have yielded to its influence, when he called the circulating 

 fluid of the Mollusca a safiies : but to call it any thing else 

 than blood is apt to lead into error ; for it possesses all the 

 essential properties of blood, flows in an analogous circle of 

 vessels, and answers the same purposes in the system. 



The circulating system of the Mollusca consists of a heart, 

 either single, or with its parts disjoined ; and of two kinds of 

 vessels, viz. arteries and veins : and the latter are supposed to 

 perform the additional function of absorbents ; for nothing 



analogous to these has been 

 yet detected. The heart is 

 very various in point of 

 figure, but is always evi- 

 dently muscular, and has its 

 interior strengthened with 

 fleshy cords (columnae car- 

 nese), interlaced in every 

 direction, (^g, 24. *) It is 

 placed in general in the 

 back, above the alimentary 

 canal, near to or between 

 the branchiae, and in a cavity 

 usually called the pericardi- 

 um, and considered, accord- 

 ing to Blainville errone- 

 ously (Manuel de Malaco- 

 logie. Sec, p. 13L), as the 

 representative of the same sac in the vertebrate animals. The 



* Interior view of the heart of Octopus vulgaris, from Cuvier. a, The 

 aorta j b, branchial veins ; c, the valves ; d, columnae carneas. 



