io 4 PHYLUM PROTOZOA- -THE SIMPLEST ANIMALS. 



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, 

 such as Protomyxci) 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 Sporozoa and Infusorians. 



SYSTEMATIC SURVEY. 



A. Primitive forms. Under this heading may be included two 

 classes : (i) the Proteomyxn, primitive, insufficiently known forms often 



FIG. 46. Diagram of Protomyxa aitrantiaca. After Haeckel. 



i. Encysted ; 2. Dividing into spores ; 3. Escape of spores, at first 

 flagellate, then amoeboid ; 4. Plasmodium, formed from fusion of 

 small amoebae. 



without a nucleus, and (2) the Mycetozoa, organisms with somewhat 

 complex fructifications, often classed as plants allied to Fungi. As 

 examples of the Proteomyxa, we have the interesting Protomyxa in four 

 phases : (a) encysted and breaking up into spores, which (b) are briefly 

 flagellate, (c) sink into amoeboid forms, and (d) flow together into a 

 composite " plasmodium 5; ; Vampyrella, parasitic on fresh- water Algoe ; 

 and many others. 



The Mycetozoa are well illustrated by Fuligo or sEthalium septic um, 

 " flowers of tan," found in summer as a large plasmodium on the bark 

 of the tan-yard. The coated spores are formed in little capsules which 

 rise from the surface of the plasmodium. The spores may be first 

 flagellate, then amoeboid, or amoeboid from the first ; the characteristic 

 plasmodium is formed by the fusion of the amcebre. 



B. Predominantly Amoeboid Protozoa. Rhizopoda. The 

 simplest Rhizopods generally resemble Ama'ba, and are ranked in the 

 class (3) Lobosa. They may reproduce simply by division, as does AniKba 

 itself, or may liberate several buds at once (Arcella), or more rarely 

 form spores (Peloinyxa}. Various forms, such as Airella, are furnished 

 with a shell. In Magosphara (Catallacta), described by Haeckel, the 



