Bacillaria.] THE INFUSORIA. 195 



form of a two-lobed disc or table. Whether a lobe can 

 be regarded, separately from its companion, as a distinct 

 organism, is not determined, but by cutting or destroying 

 the one the other empties itself at the same time, although 

 the lorica appears detached in the middle. No openings 

 have been seen in the ends, as in Micrasterias, but it is 

 probable such exist in the middle, where they are con- 

 nected. The lorica is membranous, firm, colourless, and 

 combustible ; it contains the crystalline and contractile 

 body of the animalcule, filled with green granules. Its 

 propagation by self-division is peculiar and highly interest- 

 ing. (See Jig. 123.) The middle elongates, from which 

 two new ones are formed, one uniting and forming the 

 companion to one of the old ones, and the other producing 

 the same with the remaining old one, when the newly- 

 formed individuals separate, and two pair is the result. 

 From this method of self- division, specimens, having 

 unequal lobes, are produced, by some accidental rupture, 

 before the new ones in the middle are fully developed. 

 All the species are found among conferva. 



199. EUASTBUM rota. The wheel Euastrum has a binary 

 body, lenticular and disc-like in shape, as shewn in the 

 engraving, fig. 121 and 122 ; the first being a flat, and the 

 other an edge view. Figure 123 shews the mode of 

 increase. The surface is smooth, the margin dentated or 

 spinous, the number of teeth varies from twenty-eight to 

 fifty-four ; they are either obtuse or double-pointed ; at 

 the centre an opening appears to exist on each side, close 

 to which, internally, are very minute moveable bodies, 

 as in Closterium. The portions of the binary body are 

 seldom symmetrical, one being larger than its companion. 



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