134 GENERAL HISTORY OE THE INFUSORIA. 



Few details, excepting those comprehended in attempted generic and specific 

 characters, have been published by observers on the genera of Monadina in 

 general. Uvella, AntliopTiysa, and Polytoma have, however, received more 

 attention than the rest ; and the results arrived at we wiU here abstract. 



Uvella is, in the system of Ehrenberg, characterized by the aggregation of 

 numerous Monads (XYIII. 3), severally imdistinguishable from simple isolated 

 species (XYIII. 4), into spherical or mulberry-like masses, freely moveable in 

 the surrounding liquid. The individuals, hke those of the genus Monas, have 

 a locomotive organ, consisting perhaps of two cilia, situated close to the 

 mouth at the anterior extremity, but neither tail nor eye-speck. They pro- 

 gress in the dii-ection of the longer axis of the body, and are capable of com- 

 plete self- division. In the best-examined species, U. glaucoma, Ehrenberg 

 represented large internal vesicles, a double filiform proboscis, and a great 

 number of small coloiuiess granules, conceived to be ova, lying between the 

 nutritive sacs. He supposed it to propagate both by transverse and longitu- 

 dinal self-fission, and stated that, on feeding it with indigo, as many as twelve 

 stomachs were filled, and that sometimes little blue particles like imdigested 

 matter might be seen voided from its mouth, and, lastly, that he had dis- 

 cerned several green Monads within its body, which it had eaten, and which 

 proved it to subsist on prey directly transmitted into its interior. Indi\idual 

 Monads, he added, can detach themselves from the mass, live apart for a time, 

 and again become members of the colony. 



This accoimt was rejected by Dujardin, who denied the existence of a 

 mouth, of gastric cells, and of ova, and doubted the occurrence of true self- 

 division. He likewise never witnessed the re-attachment into masses of the 

 Monadiform individuals after being once separated, but beheved that the re- 

 union of certain Monads, occasionally observed in infusions rich in these beings, 

 is a fortuitous result of the glutinous nature of their siu^face. 



These strictures of Dujardin are, without doubt, in general very just. The 

 supposed mouth is the clear space seen at the anterior extremity of most 

 unicellular organisms, whilst the supposed stomach-sacs are no other than 

 chlorophyU-vesicles or, otherwise, vacuoles. The green Monad-like cells seen 

 by the Berlin micrographer were probably starch- or chlorophyU-ceUs, or, it 

 may be, gonidia ; and it was a mere assumption to represent them as swal- 

 lowed particles. 



Itzigsohn, Cohn, and Mr. Busk make Uvella, or at least an organism like 

 it in all essential external features, a phase of existence of vegetable struc- 

 tures, — the first-named of Oscillatoria (J. M. S. 1854, p. 190), the second of 

 Protococcus, the last of Volvox. Itzigsohn describes the Euglena-i^'hase of 

 Oscillatoria as breaking up into microgonidia which collect themselves in colo- 

 nies, resembling, according to the presence or absence of coloured contents, 

 Uvella atomus, U glauca, Bodo, &c. Cohn's views are sufficiently represented 

 in our remarks on Protococcus (see p. 124), and need not be here repeated. 

 Busk represents the ciliated zoospores of Volvox {T. M. S. i. p. 39) as sub- 

 dividing into minute ciliated cells {i. e. microgonidia), which " form by their 

 aggregation a discoid body, in which the separate fusiform cells are connected 

 together at one end, and at the other are free, and furnished each with a 

 single cilium. In this stage these compound masses become free and swim 

 about in the water, constituting in fact a species of the genus Uvella, or of 

 Syncrypta of Ehrenberg." If these representations be correct, Uvella is but 

 a phase of existence of Volvocina and of Oscillatoria, and probably of other 

 plants. If this be not allowed, then the alternative remains, of supposing 

 both a vegetable and an animal organism partaking like characters and 

 qualities. 



