102 PROTOZOA THE SIMPLEST ANIMALS. 



abundant in Fishes ; the Coccidia found in most animals ; the Sarco- 

 sporidia inside muscle fibres, especially of Mammals ; the Hsemosporidia 

 inside red blood corpuscles, are all classed as Sporozoa. It is probable 

 that the organisms which cause pebiine and malaria are classifiable 

 here. 



D. Predominantly active forms (ciliate and flagellate), 

 generally called Infusorians. — Protozoa, with a definite rind and 

 with 1-3 undulating flagella, are included as (9) Flagellata, a very 

 large group, among which are such familiar forms as the common 

 Euglena of ponds ; the Monads ; Volvox, a colonial form ; Codosiga, a 

 colony in which the individual cells are furnished with a collar. 



Modified flagellate forms are included in the groups (10) Dino- 

 flagellata and (n) Rhynchoflagellata, in both of which there are two 

 flagella, differently placed in the two cases. In the first are included 

 Peridinium and Ceratium ; in the latter, the large phosphorescent 

 Noctiluca. 



As (12) Ciliata are included a very large number of forms, more or 

 less closely resembling Paramcecium, and very abundant in infusions ; 

 some, such as Opalina, in the intestine of the frog, are parasitic. The 

 cilia often vary in size and distribution, and constitute a basis of 

 classification. 



As specially modified Ciliata are included (13) Acinetaria, highly 

 specialised forms, ciliated when young, but usually furnished when adult 

 with suctorial tentacles. They are fixed in adult life, and feed on other 

 Protozoa. As examples may be given Acineta ; Dendrosoma, forming 

 branched colonies ; and Ophryodendron, without suctorial tentacles. 

 Some, like Sphcerophrya, are minute and parasitic. 



General Notes on the Functions of Protozoa. 



Movement. — The simplest form of movement is that 

 termed amoeboid, as illustrated by an Amoeba. In ordinary 

 conditions it is continually changing its shape, putting forth 

 blunt lobes and drawing others in. With this is usually 

 associated a streaming movement of the granules. A more 

 defined contraction, like that of a muscle cell, is illustrated 

 in the contractile filament of the stalk of Vorticella and 

 similar Infusorians ; and not less definite are the movements 

 of cilia and flagella, by means of which most Infusorians 

 travel swiftly through the water. Cilia in movement are 

 bent and straightened alternately, while flagella, which are 

 usually single mobile threads, exhibit lashing movements 

 to and fro. 



Considered generally, the movements are of two kinds: either (1) 

 reflex, i.e. responses to external stimulus, as when the Protozoon moves 

 towards a nutritive substance ; or (2) automatic, i.e. such movements as 



