RHIZOPODA. 761 



All the Rotifers have a marvellous fund of vitality, and survive under circumstances 

 where animals less tenacious of life would die a thousand deaths. They have been 

 thoroughly dried by means of chemical acid, wetted and restored to life, dried again, 

 wetted again, and subjected to this treatment through many successive alternations, 

 without perishing. 



THE right hand figure in the illustration represents a creature which is a good example 

 of those Rotifers, which are fixed to one spot by the extremity of the body. At 

 first sight, this animal bears a strong resemblance to several of the Molluscoids ; but a 



Rotifer eitrinus. Stephonoceros EicMwnii. 



closer examination shows that the apparent tentacles are nothing more than extensions 

 of the lobes on which the cilia are set, and the apparent cell is no cell at all, but a 

 gelatinous, secretion from the body. In one genus, however, a veritable tube is built 

 up, composed of particles of solid matter, formed into little pellets by a special organ, 

 and then deposited upon the edge of the tube. The organ which forms these pellets 

 is set towards the front of the head, and on its under side, and looks like a little revolv- 

 ing disc. 



RHIZOPODA. 



THE whole arrangment of the beings which we are now about to examine is still very 

 obscure, and the best zoologists of the present time have declared that any system which 

 has been hitherto adopted can only be considered as provisional. 



Some writers, for example, unite the Rhizopoda with the Infusoria, while others rank 

 them among the Polyzoa ; and others again consider them to be intermediate between 

 the radiata and those simple forms of animal life which are appropriately named 

 Protozoa. After taking into consideration the various systems that have been pro- 

 pounded by different authors, I have come to the conclusion that, at all events, as a 

 provisional arrangement, the Rhizopoda ought to be ranked as a distinct class, and 

 placed in the position which they here occupy. 



The name Rhizopoda is of Greek origin, and literally signifies " root-footed." It is 

 a very appropriate title, inasmuch as they put forth certain filamentous appendages 

 from their bodies, which look very like the tender rootlets of plants, and serve a double 

 purpose, namely, as organs of progression, and as instruments whereby they may catch 

 their prey. 



Some of these beings are quite unprotected, their soft, gelatinous bodies being devoid 

 of any covering ; others are inclosed in a horny case, pierced with openings, through 



