MonadinaJ] infusorial animalcules. 121 



other genera are bo likely to be mistaken for them ; for instance, 

 the young of the Bacterium, Vibrio, Uvella, Pohjtoma, Pandorina, 

 Gonium, &c., when they have separated from their clusters, or 

 issued from their common envelopes. And this difficulty in discri- 

 minating them wiU be more likely to happen when they are not 

 observed, whilst undergoing the process of self-division, or when 

 seen in water containing but a small number of them; in which 

 cases, however anxious we may be to ascertain their name, we must 

 often rest contented with an approximation to the truth. When 

 the water swarms with the creatures, the decision will be far easier, 

 and more to be relied upon, as the characters are then more easily 

 discoverable from the numerous vital relationships presented to us. 

 The obser^'er may, however, be guided to a certain extent by the 

 following rule : — Suppose that in a drop of water containing species 

 of the genus Vibrio, Bacterium, Uvella, or Polytoma (easily distin- 

 guished by their clustering forms), separate Monad-like bodies 

 were to be observed ; the probability is that they would be either 

 single forms, or the yoimg of these clustering animalcules, and if 

 there were no great difference in the size of the separate individuals 

 and those forming the clusters, this conclusion would be generally 

 correct ; and this rule applies equally to those green Monad-like 

 creatures found amongst Pandorina and Gonia. The young of the 

 CMamidomonas puhisculus is very deceptive, and may often be mis- 

 taken for an illoricated and eye-less green Monad. 



The onl)- locomotive organ which has been discovered in the 

 Monad genus is the single filiform proboscis issuing from near the 

 mouth. The numerous cilia sometimes apparent thereabouts are 

 nothing more than this proboscis in a state of vibratory or rotatory 

 motion. This organ, Ehrenberg observes, has a twofold office to 

 perform, the one being locomotive, and the other to provide the 

 creature with food ; hence I have called it a purveying organ. 



The nutritive apparatus is readily seen in some of the species in 

 its natural state (instance the M. guttula and M. vivipara), without 

 the aid of coloured food ; in others {M. termo, M. guttula and M. 

 gocialis), it may be demonstrated by the latter means. It consists of 

 several distinct or separate cells (from eight to twenty) which are 

 not all filled at the same time, and which are, for the most part, 



k: 



