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discovered by Prof. Huxley in Waldheimia and Rhynchonella, arid 

 which was found attached to the stomach in all the Brachiopoda ex- 

 amined. It is composed of two layers, the inner distinctly mus- 

 cular, the outer transparent and homogeneous. Connected with this 

 heart are vessels or blood-channels (particularly described in the 

 Memoirs) ; the " venous canals," which open into it anteriorly, 

 returning the blood conveyed by the posterior arterial channels into 

 the system of peripheral sinuses originally described by Prof. Huxley. 



Accessory " hearts " or pulsatile vesicles have been found in some 

 of the articulated Brachiopoda ; the mantle and the walls of the body 

 are essentially composed of a plate of substance traversed by reticu- 

 lated lacunae, and lined upon each side with epithelium. After ex- 

 plaining at length the distribution of the lacunae throughout the 

 mantle, the sheath of the intestine, its bands, the genital folds, the 

 arms, &c., the author proceeds to give the following sketch of the 

 course of the circulation : 



" Having now gone over all that I have been able to ascertain with 

 respect to the central and peripheral portions of the circulatory appa- 

 ratus, and having also examined the lacunes and blood-canals of the 

 brachial organs, it will not be difficult to follow the flow of the blood 

 throughout its entire course in Waldheimia ; and as it is in it, so 

 will it be in all probability in all other Brachiopods. 



" It has been shown that the heart is a simple, unilocular, pyri- 

 form vesicle, suspended from the dorsal aspect of the stomach, and 

 projecting freely into the perivisceral chamber ; that there is neither 

 auricle nor pericardium, unless the membrane which closely invests 

 it can be so called, that it is hardly more complex in structure than 

 the pulsating vessel of the Tunicata ; and that in Lingula, indeed, 

 it scarcely at all differs from the heart of these lowly organized mol- 

 lusks. This vesicle, or heart, propels the blood through four arterial 

 trunks or channels, to the reproductive organs and mantle, and pro- 

 bably also to the alimentary tube, and is apparently assisted by four 

 or more pulsating vesicles in connexion with these principal trunks. 

 The blood thus conveyed by the genital or pallial arteries will escape 

 by the lacunes in the membranes suspending the genitalia, into the 

 plexus in the floor of the great pallial sinuses. Thence it will find 

 its way into the outer lacunary system of the pallial lobes, and into 

 that of the dorsal and ventral walls of the body, as well as into the 



