i PROTOZOA 33 



in forming submarine deposits. In their case too the dead and disin- 

 tegrating bodies rain slowly down through the depths of the ocean. 

 But the silica of their skeleton is much less soluble than the calcium 

 carbonate of the Foraminifera. Consequently in deep regions of the 

 ocean where both Foraminifera and Radiolaria are constantly sinking 

 down from the surface layers the skeletons of the former are removed by 

 solution before they reach the bottom wfiile those of the latter persist 

 and are deposited to form Radiolarian ooze. Deposits of fossil radiolarian 

 ooze are found amongst the rocks of various parts of the world, as 

 for example the comparatively modern deposits in Barbados and some 

 of the flinty " cherts " which occur here and there amongst the more 

 ancient rocks. 



Glancing back over the Protozoa so far described we note that they 

 possess this great characteristic in common that the outer layer of their 

 protoplasm is soft and can be pushed out to form pseudopodia, and 

 further, that they ingest food in the form of solid particles. These 

 features unite them together in a group the SARCODINA. 



II. FLAGELLATA 



In contrast with the Sarcodina the members of the next group the 

 FLAGELLATA have the surface layer of their protoplasm more or less 

 condensed to form a smooth bounding layer which is incapable of being 

 pushed out into pseudopodia. We will first review the characters of 

 three different genera of Flagellata which are easily obtained for laboratory 

 study and thereafter consider certain genera which have been discovered 

 within recent years to be of great practical importance as causes of disease 

 in man and domestic animals. Two of the three genera first mentioned 

 are characterized by their bright green colour due to their containing 

 chlorophyll, the colouring matter which occurs in ordinary green plants, 

 and the first of them often exists in freshwater puddles in such numbers 

 that the water is throughout quite green and opaque* 



EUGLENA 



Euglena (Fig. 14) is a comparatively small creature (the commonest 

 species E. viridis about 55 //. by 15 /A), somewhat spindle-shaped with 

 one end blunt and the other pointed. Its smooth surface dips inwards 

 close to the blunt end to form a conical funnel which expands at its apex 

 into a spherical space the reservoir (Fig. 14, r). From the funnel there 



D 



