Freshwater Bryozoa, with descriptions of new Species. 199 



attached by the other end to the base of the imperforate valve* 

 binding the parts of the hinge-joint together — a substitute in fact 

 for a ligament. In some species this set assumes in part the 

 function of an adductor muscle. 



We have then evidently some reason for supposing that the 

 Brachiopoda as well as the Ascidice are related to the Bryozoa ; 

 and it is in this way that these latter are connected with the La- 

 mellibranchiata. After a careful examination of the Brachiopoda, 

 it is impossible to doubt the connexion that exists between the 

 two great divisions of the testaceous Acephala. Indeed this is 

 evident, whether we look to the digestive organs, the vascular 

 system, or to the reproductive apparatus. It is in these animals, 

 too, that the respiratory organ is first found in connexion with 

 the mantle, — in Terehratula quite rudimentary, in Lingula to 

 some extent specialized. On comparing Anomia with Orbicula, 

 this relationship is best seen. In both the mantle is completely 

 separated, and in both it is connected with the ovary ; the large 

 oral palpi of the one form the homologue of the branchial organs 

 of the other ; and we see this relationship in the deficiency of 

 pedal organ in Anomia, and in the extensive union that still 

 subsists between its breathing apparatus and the mantle : the 

 perforation of the under-valve of both is also remarkable ; but 

 not more so than that the great muscle of both should be 

 divided, — part forming the adductor, part the adhesive disc. 



We have now endeavoured to trace the affinities of both 

 branches of Bryozoa ; one appears to pass at once into the As- 

 cidice, which, how closely soever related analogically to the Lamelli- 

 branchiata, are nevertheless removed far from them by the nature 

 of their vascular, respiratory and reproductive systems. In the 

 Mollusca the heart is always systemic, and the gill is universally 

 an appendage to the mantle. In the Ascidia? the heart is as 

 much pulmonic as systemic, and the breathing apparatus is a 

 development from the alimentary canal — is in fact pharyngeal. 

 In these respects the Ascidian deviates from the Molluscan type 

 and approximates to that of the lower Vertebrata, — the fishes, in 

 which the heart is pulmonic and the breathing organ pharyngeal. 

 The reality of this relationship is revealed by the anatomy of the 

 Lancelet so ably described by Professor John Goodsir, who has 

 pointed out the resemblance of its respiratory system to that of 

 the Tunicata. Indeed the branchial sac and vascular apparatus 

 of this curious fish almost completely resemble those organs in 

 the Ascidian. 



The other branch of the Bryozoa, comprising those with oral 

 arms, passes into the Brachiopoda ; or at least this is rendered 

 more than probable by the resemblance of the brachial organs of 

 the latter to the arms of the former, and by the similarity of the 



