753 



CHAPTER XIJI 



ANIMALCULES INFUSORIA AND EOT IF K 1 1 I 



NOTHING can be more vague or scientifically inappropriate than the 

 title Animalcules ; since it only expresses the small dimensions of 

 the beings to which it is applied, and does not indicate any of their 

 characteristic peculiarities. In the infancy of microscopic know- 

 ledge, it was natural to associate together all those- creatures which 

 could only be discerned at all under a high magnifying power, and 

 whose internal structure could not be clearly made out with the 

 instruments then in use; and thus the most heterogeneous assem- 

 blage of plants, zoophytes, minute crustaceans, larva' of worms, 

 molluscs, &c.. came to be aggregated with the true animalcules 

 under this head. The class was being gradually limited by the 

 removal of all such forms as could be referred to others ; but still 

 very little was known of the real nature of those that remained in 

 it until the study was taken up by Professor Ehrenberg. with the 

 advantage of instruments which had derived new and vastly im- 

 proved capabilities from the application of the principle of achro- 

 matism. One of the first and most important results of his study, 

 and that which has most firmly maintained its ground, notwith- 

 standing the overthrow of Professor Ehrenberg's doctrines on other 

 points, was the separation of the entire assemblage into two distinct 

 groups, having scarcely any feature in common except their minute 

 size, one being of very lon\ and the other of comparatively Ji/ti/Ji 

 organisation. On the lower group he conferred the designation of 

 Polygastrica (many-stomached), in consequence of having been led 

 to form an idea of their organisation which the united voice of t In- 

 most trustworthy observers now pronounces to be erroneous ; and 

 as the retention of this term must tend to perpetuate the error, it- 

 is well to fall back on the name Infusoria, or infusory animalcules, 

 which simply expresses their almost universal prevalence in infusions 

 of organic matter. To the higher group Professor Ehrenberg's 

 name Rotifrra or Rotntorin is, 011 the whole, very appropriate, as 

 significant of that peculiar arrangement of their cilia upon the 

 anterior parts of their bodies, which, in some of their most common 

 forms, gives the appearance (when the cilia are in action) of wheels 

 in revolution ; the group, however, includes many members in which 

 the ciliated lobes are so formed as not to bear the least resemblance 

 to wheels. In their general organisation these ' wheel-animalcules' 

 stand at a much higher level than the unicellular Infusoria, but it 



3 c 



