io6 PROTOZOA. 



rocks of the Carboniferous and several subsequent epochs. The 

 famous Eozoon canadeuse of Cambrian rocks is regarded by most as a 

 purely mineral formation. 



There seem at least to be sufficient relics to warrant Neumayr's 

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

 irregularly agglutinated particles (Astrorhizidae), 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 Amoeba. 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 Amoeba, 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, i.e., responses to external stimulus, as when the Protozoon moves 

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

 appear to 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 Amoebse with the movements of drops of 

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



