ROTIFERA. 759 



we must restrict ourselves to its chief peculiarities. Placed among the ordinary polype- 

 cells may be seen, at certain times of the year, a few scattered egg-shaped objects, 

 some eight or ten usually being found on a branch. Within these cells are seen a 

 small number of very minute living beings, which gradually develop themselves. A 

 restless movement prevails towards the upper part, some slender tentacles make their 

 appearance at the end, and at last the whole of the tip breaks loose, displaying itself 

 as a tiny medusa. 



This change is indeed a wonderful one, perhaps even more marvellous than the 

 mutual transformations of hydra tuba, and medusa, inasmuch as the Campanularia and 

 the medusa belong absolutely to separate classes ; and that a medusa should spring from 

 a zoophyte is hardly less surprising than that a perch should give birth to a human being. 



These important discoveries were made simultaneously by Professor Van Beneden 

 and Sir John Dalyell, and the former naturalist was able to observe a phenomenon 

 which certainly seems to be the first step towards the return from the medusa into the 

 zoophyte. Having isolated a specimen of the little medusae, and made a careful 

 drawing of it, he left it for about an hour, and on his return was surprised to find that 

 the whole shape of the tiny being had altered. The convex disk had become concave, 

 the tentacles were reversed, and the animal had changed the central footstalk of the 

 medusa into the semblance of a zoophytic stem. 



"My observations," remarks that accomplished naturalist, as quoted by Mr. T. R. Jones, 

 " go no further ; but although I have not seen the medusa give origin to a polype stem, 

 I observed it up to the moment when it was about to form a new colony ; and without 

 fear of deceiving ourselves, we may form by analogy some idea of the changes 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 become 

 converted into true tentacles. The polype 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 disk a new aperture is formed, which communicates with the central cavity, and 

 becomes the permanent mouth, which is situated directly opposite to the original one. 



" Being now fixed by its base, the body of the polype begins to grow ; and as its ex- 

 ternal sheath becomes hardened, buds sprout at regular intervals from its surface. In a 

 word, the growth of the polype resembles that of the hydra, with this difference, that in 

 the latter there is no polype stem, and their buds sprout from another part of the body." 



The name of Campanularia is given to this zoophyte in consequence of the bell-like 

 form of its cells, and is derived from the Latin word " campana," a bell. 



THE delicate PLUMULARIA is so called on account of the feathery appearance of its 

 polypidon. The cells are always small and the egg-vesicles are scattered. In some 

 species the stem is composed of many parallel tubes, such as Plumularia myriophyllum, 

 but in the present species it is quite simple. The egg-vesicles are rather widely scattered. 



ROTIFERA. 



ALTHOUGH the Rotifera, or Wheel Animalcules, are generally placed among the 

 Infusoria, on account of their minute dimensions aud aquatic habits, it is evident, 

 from many peculiarities of their formation, that they deserve a much higher place, and 

 in all probability constitute a class by themselves. 



They are called Wheel Animalcules on account of a curious structure which is found 

 upon many of their members, and which looks very like a pair -of revolving wheels set 



