146 Royal Society : — 



which will set backwards in the direction of the membranous bands 

 connecting the alimentary tube to the parietes, and will flow through 

 their channels into the system of visceral lacunes, which encircle the 

 alimentary canal within the sheath, and which probably carry blood 

 to the liver. This current will also supply blood to the lacunes 

 nourishing the muscles. The blood thus directed will reach the 

 branchio-systemic vein, either by the great oesophageal lacunes, or 

 through the foramina which penetrate the sides of the channel as it 

 runs along the dorsal ridge of the stomach. 



''■ The other blood-current will set forward in the direction of the 

 base of the arms, and some of it will pass into these organs through 

 their general system of lacunes ; but the principal portion will be 

 carried by the afferent brachial canal to the extensive plexus of 

 lacunes in those parts, and will circulate, in the manner before 

 pointed out, within the walls of the great brachial canal. The blood 

 will then be drawn up one side of the cirri through the vessels — 

 the afferent brachial arteries — originating in the great brachial 

 plexus, and returning down the other, will be poured into the efferent 

 brachial canal, and thus reach the lateral efferent sinuses at the root 

 of the oesophagus. Thence it will enter the great oesophageal 

 lacunes, and there meeting with the other current of returning blood 

 from the visceral lacunes, will be carried to the heart by the bran- 

 chio-systemic vein along the dorsal side of the stomach. 



" Thus it is perceived that the blood finds its way back to the cen- 

 tral organ in a mixed condition. That which is conveyed by the 

 gastro-parietal and other bauds will be imperfectly aerated, ha%'ing 

 only flowed through the palUal membranes, which must be looked 

 upon as but accessory oxygenating agents. The arms undoubtedly 

 perform the office of gills, and are true respiratory organs. The 

 blood which circulates through them will consequently be returned 

 in a perfectly aerated condition, to be mixed, however, with that in 

 a less })ure state from the \-isceral lacunes before it enters the heart. 

 This mixed state of the blood is not by any means peculiar to these 

 animals, for it obtains in many of even the higlu r mollusks." 



The ])erivisccial cavity and the great pallial sinuses have no com- 

 munication with the proper blood-vascular system, but are to be com- 

 pared to the atrium of the Ascidiauida, and the water-chambers of 

 the Cephalopoda and other moUusca. The pseudo-hearts enable the 

 perivisceral cavity to communicate with the exterior, and convey 

 away the genital, and probably the renal products. On tliis head 

 the author says : — 



" From the foregoing account of the circulatory apparatus, it 

 would appear that the perivisceral chamber, and its various so-called 

 vascular ramifications in the mantle, are not connected with the 

 blood-system. This is no doubt a startling fact. I commenced the 

 present investigation fully imbued with the opinion that these parts 

 were blood reservoirs and channels, and I only relinquished it when 

 it became no longer tenable. Step by step the points relied on had 

 to be abandoned, until at length the full conviction was arrived at 

 that I had been seeking to establish a fallacy. I have been unable 



