24 THE MICROSCOPE AND ITS REVELATIONS. 



CHAPTER XL 

 ANIMALCULES. INFUSORIA AND ROTIFERA. 



411. 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 character- 

 istic peculiarities. In the infancy of Microscopic knowledge, 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 assemblage of Plants, Zoophytes, minute Crustaceans, 

 larvae of Worms, Mollusks, etc., 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 Prof. Ehrenberg, with the advantage of instru- 

 ments which had derived new and vastly improved capabilities from the 

 application of the principle of Achromatism. One of the first and most 

 important results of his study, and that which has most firmly maintained 

 its ground, notwithstanding the overthrow of Prof. Ehrenberg's doctrines 

 on other points, was )he separation of the entire assemblage into two dis- 

 tinct groups, having scarcely any feature in common except their minute 

 size; one being of very low, and the other of comparatively high organiza- 

 tion. On the lower group he conferred the designation of Polygastrica 

 (many-stomached), in consequence of having been led to form an idea 

 of their organization which the united voices of the most trustworthy ob- 

 servers 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 In- 

 fusoria, or Infusory Animalcules, which simply expresses their almost 

 universal prevalence in infusions of organic matter. To the higher group, 

 Prof. Ehrenberg's name Rotifera or Rotatoria is on the whole very appro- 

 priate, 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 organization, these * Wheel-animalcules ' must certainly 

 be considered as members of the Articulated division of the Animal King- 

 dom; and they seem to constitute a Class in that lower portion of it, to 

 which the designation Worms is now commonly given. Notwithstanding 

 the wide zoological separation between these two kinds of Animalcules, 

 it seems most suitable to the plan of the present work to treat of them in 

 connection with one another; since the Microscopist continually finds 

 them associated together, and studies them under similar conditions. 



