400 THE ANATOMY OF INVERTED RATED ANIMALS. 



The perivisceral cavity communicates with the pallial 

 chamber by at fewest two, and sometimes four {Rhynchonel- 

 la), tubular organs, which have been described as hearts,^ but 

 are now known to have no such nature. 



Each of these organs is shaped like a funnel, the wide por- 

 tion which opens into the perivisceral cavity being much plait- 

 ed and folded, and separated by a constriction from the nar- 

 rower part, which answers to the pipe of the funnel. The lat- 

 ter, passing obliquely through the anterior wall of the visceral 

 chan)ber, ends by a small aperture in the pallial cavity. Prof. 

 Morse has observed the passage of the eggs through these 

 organs in TerehratuUna septentrionalis. They are drawn 

 into the open end of the funnel by the action of the cilia with 

 which its surface is covered, and enter the pallial cavity by 

 the aperture just mentioned. It is probable that these ** pseu- 

 do-hearts " subserve the function both of renal organs and 

 of genital ducts ; and that they are the homologues of the 

 organs of Bojanus of other moUusks, and of the segmental 

 organs of worms. 



Between the ectoderm and the lining membrane of the 

 prolongations of the perivisceral cavity in the mantle, and 

 between the endoderm, the ectoderm, and the lining membrane 

 of the perivisceral cavity itself, there is an interspace broken 

 up into many anastomosing canals, which I conceive to rep' 

 resent a large part of the proper blood system. 



Vesicular dilatations of the walls of these canals found at 

 the back of the stomach, and in some other localities, in the 

 Brachiopods with articulate shells, have been regai-ded as 

 hearts; but observations on the living animals, made by various 

 investigators, show that they are not contractile, and their 

 function is unknown. Although the existence of a direct 

 communication between the perivisceral chamber and the 

 blood canals has not been demonstrated, it is very probable 

 that the perivisceral chamber really forms part of the blood- 

 vascular system. 



Muscles for the adduction and divarication of the valves 

 of the shell, and for effecting the other movements of the ani- 

 mals, are well developed in the Brachiopoda.^ They are to a 

 great extent striated. 



* Owen, *' Lettre sur Pappareil de la circulation chez les Mollusques de la 

 classe des Brachiopodes." (" Annates des Sciences Naturelles," 1845.) 



2 See Hancock {I. c). Owen, Introduction to Davidson's "Fossil Brachi- 

 opoda." ("Memoirs of the Palicontoofraphical Society," and "Transactions 

 of the Zoological Society of London," 1835.) 



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