Animalcule

[Fr., from Lat. animalculum, a little animal.] ( Zool.) The name commonly given to those minute forms of animal life only visible by means of magnifying-gla es.-Nothing can be more vague or inappropriate than this name, since it only expre es 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 knowledge, it was natural to a ociate together all those creatures whose internal structure could not be clearly made out with the instruments then in use; and thus the most heterogeneous a emblage of plants, zoöphytes, minute crustaceans, ., came to be aggregated with the true animalcules under this head. The cla 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 instruments which had derived new and vastly improved capabilities from the application of the principle of Achromatism. The most important result of his study was the separation of the entire a emblage into two distinct groups, one, the Infusoria, being of very low, and the other, the Poly gastric a, of comparatively high organization. Lately the name Rotifer a, or Rota IMG:content-0232.png:[blocks in formation] 1. IN PUS OR I A (Vorticella nebulifera). 75 times its size. 2. Sepa rate body of the same, 300 times its size; a, mouth; b, nucleus; c. contractile vesicle. 3. ROTIFER A ( Trio pht halm us dorsualis ), 300 times its size. toria , has been substituted for Poly gastric a, and a group has been separated from the Infusoria to form the lowest order of the Protozoa under the name of Rhizopod a. See INFUSORIA, ROTIFER A, and RHIZOPOD A. See also PROTOZOA.