Freshwater Bryozoa, with descriptions of new Species. 195 



ova on maturity become attached to that side of the cell which 

 is connected to the substance sustaining the polypidom. And 

 here they remain fixed, indicating the track of the various branches 

 of the Bryoozon long after its decay and disappearance in autumn. 

 The free branches however must scatter their eggs. Most likely 

 in Fredericella, too, they are dispersed, and borne away by the 

 currents on the destruction of the polypidom, which is very freely 

 branched ; and in no instance have I seen its eggs left adhering 

 to the surface of its attachment. 



Having now gone through the details of the anatomy and de- 

 velopment of the freshwater Bryozoa as far as I have been able 

 to study them during a very short but laborious investigation of 

 the subject, it is quite evident that these animals are as highly 

 organized as the marine Ascidian polypes. Plumatella and Fre- 

 dericella certainly show some interesting deviations from that 

 type ; but in Paludicella we perceive an almost complete resem- 

 blance to it ; proving the close affinity that exists, and the pro- 

 priety of uniting the whole into one group. The approximation 

 of this genus to the marine forms is evinced not only by the 

 muscular system, but likewise by the digestive apparatus ; and by 

 the bright, pellucid, horny character of the external polypidom. 

 It is also equally evident that the organization of this group is 

 very much above that of the typical Radiata. This Professor 

 Allman has already clearly demonstrated; and yet perhaps we 

 ought to hesitate before removing the Bryozoa into the subking- 

 dom Mollusca as proposed by this naturalist. 



The immediate relationship of these animals to the Ascidia is 

 too obvious to be called in question, — a relationship which has 

 long been acknowledged, though the homology of the parts does 

 not appear to be correctly understood; at least it will bear 

 another interpretation, which I am incUned to look upon as the 

 true one. Dr. Farre observes in his paper, that " in Tunicata 

 the tentacles are reduced to mere rudiments at the entrance of 

 the respiratory sac, and the cilia are distributed over the surface 

 of this cavity, which is in proportion magnified, and is analogous 

 to the pharynx of Ciliobrachiata. The more immediate entrance 

 to the alimentary canal, thence called mouth, being situated at 

 the bottom of this sac, corresponds with the part that I have 

 called cardia." 



This view of the relationship of the parts has with some 

 modifications been generally followed by subsequent writers. In 

 all the Ascidians however, there is a well-defined oesophagus, 



directions and evinced great activity, cilia densely clothing it from end to 

 end. The cell after the escape of the gemmule continued gaping ; and the 

 polype, which before was indistinctly visible, had now quite disappeared, 

 nothing but slight traces of the retractor muscles remaining. 



13* 



