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 Ascidie 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 im connexion with 
the mantle,—in Terebratula quite rudimentary, in Lingula to 
some extent specialized. On comparing dnomia 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 sce 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- 
cidie, 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 Ascidie 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 
