CLASSIFICATION OF PROTOZOA. 97 



and animal life, just across the line which separates the unicellular from 

 the multicellular, illustrating the beginning of that important distinc- 

 tion between somatic or body cells and reproductive cells, and occurring 

 in asexual, hermaphrodite, and unisexual phases. Klein records no less 

 than 24 different forms of V. aureus from the purely vegetative and 

 asexual to the parthenogenetic, for there may be almost entirely male 

 colonies, almost entirely female colonies, and other interesting transi- 

 tional stages. Klein has also succeeded to some extent in showing 

 that the occurrence of the various reproductive types depends on outside 

 influences. 



General Classification of Protozoa. 



Since the Protozoa are unicellular organisms (except 

 the few which form loose colonies), their classification 

 should be harmonious with that of the cells in a higher 

 animal. This is so. Thus (a) the Rhizopods, in which 

 the living matter flows out in changeful threads or 

 "pseudopodia," as in the common Amceba, are compar- 

 able with the white blood corpuscles or leucocytes, many 

 young ova, and other "anweboid" cells of higher animals; 

 (b) the Infusorians which have a definite rind and bear 

 motile lashes (cilia or flagella), e.g., the common Paramoecium, 

 may be likened to the cells of ciliated epithelium, or to the 

 active spermatozoa of higher animals ; (c) the parasitic 

 Gregarines which have a rind and no motile processes or 

 outflowings, may be compared to degenerate muscle cells, 

 or to mature ova, or to "encysted" passive cells in higher 

 animals. 



This comparison has been worked out by Professor Geddes, who also 

 points out that the classification represents the three physiological 

 possibilities (a) the amoeboid units, neither very active nor very passive, 

 form a median compromise ; (b) the ciliated Infusorians, which are 

 usually smaller, show the result of a relative predominance of expendi- 

 ture ; (c) the encysted Gregarines represent an extreme of sluggish 

 passivity. 



But, as Geddes and others have shown, the cells of a higher animal 

 often pass from one phase to another, the young amoeboid ovum 

 accumulating yolk becomes encysted, the ciliated cells of the windpipe 

 may, to our discomfort, sink into amoeboid forms. The same is true of 

 the Protozoa ; thus in various conditions the ciliated or flagellate unit 

 may become encysted or amoeboid, while in some of the simplest forms, 

 3uch as Protomyxa, there is a " cell" cycle " in which all the phases occur 

 in one life history. 



It is also important to notice Professor Ray Lankester's division of 

 the Protozoa into naked and corticate forms (Gymnomyxa and Corticata). 

 The Gymnomyxa include the primitive forms and the Rhizopods ; the 

 Corticata include the two extremes Gregarines and Infusorians. 



7 



