CIRCULATION IN TEREDO. 



213 



Fj . 4Q 





veins of the same name begin ; 

 and, running in a contrary di- 

 rection, they ultimately reach 

 the large longitudinal veins 

 into which they pour the re- 

 fluent fluid. This enters into 

 the two auricles, thence into 

 the only ventricle, whence it 

 is carried and distributed 

 throughout the body by means 

 of the arterial channels which 

 lead away from that ventri- 

 cle.* 



As it offers some exceptions 

 to this account of the distri- 

 bution of the bloodvessels in 

 the Conchifera in general, I 

 am tempted to extract for you 

 the interesting description of 

 the circulation in Teredo na- 

 valis, as given by Sir Everard 

 Home: "The heart," he 

 says, "is situated upon the 

 back of the animal, near the 

 head, consisting of two auri- 

 cles (Fig. 40 f), of a thin, dark- 

 coloured membrane ; the auri- 

 cles open by contracted val- 

 vular orifices into two white 

 strong tubes ; these, united, 



* Journ. de Physique, Ixxxix, 133. 

 See also Garner in Charlesw. Mag. 

 N. Hist. n. s. iii. 167. 



t Figure of Teredo navalis, show- 

 ing the heart and other internal organs, 

 of the natural size, exposed in a pos- 

 terior view, a a, The boring-shells, 

 separated and turned back ; b, the di- 

 gastric muscle ; c, the intestine pass- 

 ing over it ; d d, the testicles ; e e, the 

 auricles of the heart \ff, the ventri- 

 cle ; gg, the artery going to the head ; 

 h h, the vessels from the branchiae 

 going to the heart ; i i, the branchiae 

 or gills ; k k, ducts of the testicles, 

 traced through their course ; / /, a 

 strong substance, with transverse fibres, 

 having a pile upon it, to strengthen this, the weakest part of the animal. 



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L II 



