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XXI. Oil the Fhijsiolor/u of the Tallied Sinuses of the Brachiopocla. By JoHX D. Mac- 

 DONALD, R.N., F.B.S. Communicated hy George Busk, Esq., F.B.S., Sec. Z.S. 



Read April 18th, 1861. 



i. O Mr. Hancock and Professor Huxley belongs the credit of having first cast a doubt 

 on the nature and office of the so-called Cuvierian hearts of the B^'achiopoda ; and should 

 any further evidence be required to sustain the truth of the position ultimately laid down 

 by those original observers, I have to announce my discovery in Lingula, of a determinate 

 circulation of spherical and violet-tinted corpuscles (fig. 6) in all tlie ramifications of the 

 pallial sinuses (Plate XXXV. fig. 4), not depending upon the contractions of a propulsory 

 cavity, but upon the undulations of a ciliated lining. It, moreover, presented this charac- 

 teristic peculiarity, that an onward and a returning ciirrent are at the same time visible in 

 each canal, as shown by the direction of the arrows in fig. 4. 



The white lines which are described as running upon the outer wall of the pallial 

 sinuses of Lingula, and about which so much misconception appears to have existed in 

 the mind of Vogt, are nothing more than the septa more or less perfect (fig. 4, a), which 

 serve to direct as well as to obviate the friction of two ciliary currents passing in opposite 

 directions in the same vessels. Mr. Hancock's reasoning against Vogt's opinion, that 

 these are vascular ramifications, is simple and conclusive ; but, of their real nature as just 

 pointed out, I can entertain no doubt whatever. 



The four Cuvierian hearts of Bhynchonella, singularly enough, have given place to the 

 five contractile vesicles of Mr. Hancock ; and if these latter, mth the vessels connected 

 T^dth them, be not really homologous with the water-vascular system of the Anmiioida, 

 the coincidence in the same animal of another and a purely ciliary circulation in which 

 coloured corpuscles, developed for that special purpose, seem to perform the office of blood- 

 globid.es, is not a little interesting. 



In some of the Beroidce the sinus system exhibits a remarkably beautiful ciliary cii'cu- 

 lation of a corpusculated fluid, and the ovaria occupy the walls of those ramified and reti- 

 culated canals, so much after the fashion of those of the Brachiopod, that the homologies 

 of the two systems can scarcely be doubted. There is this difference, however, that in the 

 Beroidce, the main trunks of the sinuses, which form the equivalent of the common 

 cavity, so called, of the true Polypi, open directly into the stomach ; whereas this com- 

 munication is altogether cut off in the Brachiopod, and the escape of the ova is pro^dded 

 for by the external openings so clearly demonstrated by Mr. Hancock in the organs pre- 

 viously recognized as hearts. The question arises, Is this difference sufficient to destroy 

 the homology here indicated ? As well might it be said that the absence of an anal out- 

 let to the alimentary canal of JFaldheimia militated against its homology with that of 

 lAnguIa ; or, that the open water-vascular-system of Distoma had no equivalent in the 



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