134 THE AQUARIAN NATURALIST. 



which must necessarily occur. The Campanularia in 

 its Medusa-state has only a single aperture, situated 

 at the extremity of its central pedicle. We have 

 already seen that its body becomes inverted like the 

 finger of a glove, and that the marginal filaments be- 

 come converted into true tentacles. The polyp fixes 

 itself by the extremity of its central appendage, that 

 is, by what was previously its mouth. The back of 

 the umbrella becomes depressed at the same time 

 that the tentacles change their direction, and in the 

 centre of the disc a new aperture is formed, which 

 communicates with the central cavity, and becomes 

 the permanent mouth, which is situated directly op- 

 posite to the original one. Being now fixed by its 

 base, the body of the polyp begins to grow ; and as its 

 external sheath becomes hardened, buds sprout at 

 regular intervals from its surface. In a word, the 

 growth of the polyp resembles that of the Hydrae, 

 with this difference, that in the latter there is no 

 polyp- stem, and their buds sprout from another part 

 of the body." 



Such is Van Beneden's " idea derived from ana- 

 logy." We shall be delighted if any of our readers 

 should fortunately have a favourable opportunity of 

 putting science in possession of the real proceeding of 

 Nature in this matter. 



