474 POLYZOA 



These results did not hold good for all the zooecia in a single 

 colony. In some, the " brown body " was not completely got rid 

 of at the end of sixty-eight days, the conclusion of the experiment. 



So striking are the facts relating to the " brown bodies " that 

 it has been believed 1 that what we have above described as the 

 individual really consists of two kinds of individuals : firstly, 

 the " polypide " or complex of tentacles and digestive organs ; 

 and secondly, the " zooecium," or house of the zooid or polypide, 

 corresponding with what has been described above as the body- 

 wall. The one individual, the zooecium, is on this view provided 

 with successive generations of the second kind of individual, the 

 polypide ; and these latter function as the digestive organs of 

 the two-fold organism. This view, though fascinating at first 

 sight, is not borne out by an examination of all the facts of the 

 case, especially when the Entoprocta are taken into account. 



History. The history of the Polyzoa, as far as. 1856, has 

 been fully treated by Allman in his great work on the Fresh- 

 water Polyzoa ; 2 but a few words may be said on this subject. 



The Polyzoa attracted comparatively little attention before 

 the beginning of the present century. Originally passed over as 

 seaweeds, their real nature was established in connexion with 

 the discovery of the animal nature of corals. So great a revolu- 

 tion could hardly be accepted without a struggle, and even 

 Linnaeus went no further in this direction than to place them 

 in a kind of half-way group of " zoophytes," whose nature was 

 partly animal and partly vegetable. It is hardly necessary to 

 point out that this view has now been abandoned by common 

 consent ; and indeed there is no more reason for regarding an 

 animal as showing an approach to the plants because it grows 

 in the external semblance of a seaweed than there would be for 

 supposing a bee-orchid to be allied to the animal kingdom 

 because of the form of its flowers. 



But the claims of the Polyzoa to rank as a separate class 

 were by no means admitted with the discovery that they were 

 animals. They were still confounded with Hydroids, Alcyo- 

 narians, or Corals until their possession of a complete alimentary 

 canal was recognised as a feature distinguishing them from those 



1 See especially G. J. Allman, Monograph of the Fresh-water Polyzoa, Ray Society, 

 1856, p. 41 ; and H. Nitsche, Zeitschr. wiss. Zool. xxi. 1871, p. 479. 



2 Ray Society, 4to, 1856. 



