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JBORTY- FIFTH REPORT ON THE 8 TATE MUSEUM. 



only an outer but a smaller inner series of branches. The main 

 trunks of the pallial sinuses are the receptacles of a portion of 

 the genital organs, but this fact does not interfere with their 

 circulatory function. Similar canals traverse the fleshy brachia 

 for their entire length. In Lingula there are three of these lying 

 side by side ; one very large and central, a much smaller one at 

 the base of the cilia, the third being lacunary and lying in the 

 brachial fold. In Crania and Hhynchonella the last- 

 mentioned of these is absent. All the vascular sinuses pass into 

 the perivisceral chamber and are developed into vescicular 

 dilatations at the back of the stomach and elsewhere. These bodies 

 are not contractile, and their function is at present unknown 



Fig. 137.— A portion of the circulatory system in Magellania venosa. Above the right is the 

 ciliated oral surface 04), the stomach and intestine (j), upon whose dorsal surface is situated 

 a central heart (a) sending an aorta (c) to the brachia, and giving off two lateral branches, 

 each of which bears a pulsatile sac or subsidiary heart (6). The lateral vessels (d) supply 

 the genital gland (/), and terminate (g) within the peripheral lacune (t) lying at the base of 

 the setae (7?) which border the mantle (K). (Joubin.) 



(Huxley). There is no pulsatile vesciclein the animal which per- 

 forms the function of a heart, and circulation seems to be main- 

 tained by means of the ciliated tissue with which the sinuses are 

 lined. Although there is no communication between these ves- 

 sels and the walls of the perivisceral chamber, it is the opinion 

 of some authors (Huxley) that these walls, which are also 

 ciliated, contribute to this function. 



In Lingula, Morse has observed the existence of caeca! exten 

 sions of the sinuses or arrypullcB scattered over the inner surface 

 of the mantle, which arehighly contractile and receive and dis- 

 charge the circulating fluid with perfect regularity. 



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