io6 PROTOZOA. 



rocks of llie Carljoniferous and several suljsequenl epochs. The 

 famous Eozoon canadeiisc of Cambrian rocks is rej^'arded by mrist as a 

 purely mineral formation. 



There seem at least lo be sufiicient relics to warrant Neamayr's 

 generalisation in regard to Foraminifera. that the earliest had shells of 

 irregularly agglutinated particles (Astrorhizida;), that these were suc- 

 ceeded by forms with regularly agglutinated shells, exhibiting types of 

 architecture which were subsequently expressed in lime. 



Relics of siliceous Radiolarian shells are also known from Silurian 

 strata onwards, with, perhaps, the exception of the Devonian. Best 

 known are those which form the later Tertiary deposits of Barbados 

 earth, from which Ehrenberg described no fewer than 278 species. 



GENERAL NOTES ON THE PROTOZOA. 



Ordinary Functions — Movement. — The most obvious 

 function of a Protozoon is movement, of which the simplest 

 mode is that termed amoeboid. This is well illustrated by 

 an Anixba. In ordinary conditions it is continually chang- 

 ing its shape, putting forth blunt lobes and drawing others 

 in. With this is usually associated a streaming movement 

 of the granules, while within the cell itself a somewhat 

 similar streaming is often seen, as in many plant cells. 

 Besides the local changes of form seen in the Anicuba, a 

 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, and are thrown into serpentine waves during 

 these movements." 



Considered generally, the movements are of two kinds ; either (i) 

 reflex, ;'.«., responses to external stimulus, as when the Protozoon moves 

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

 appear lo originate from within, without our being able to point to the 

 immediate stimulus, e.g., the rhythmical pulsations of contractile 

 vacuoles. 



While all vital activity or life must remain inexplicable in lower 

 terms until we know the chemical nature of protoplasm, it is useful to 

 compare the movements of Amivline with the movements of drops of 

 fine emulsion, as Professor Biilschli has done in great detail. For in this 



