SARCODINA. 17 



represent genera existing at the present day. What countless 

 myriads of these microscopic organisms must be present in the 

 chalk rocks of our North and South Downs alone, when we 

 consider that thousands go to the square inch. 



The Protozoa are divided into four classes : (1) the Sarcodina, 

 (2) Masiigophora, (3) Sporozoa, (4) Infusoria. 



Sarcodina are protozoa in which the protoplasm is naked and 

 which have no permanent organs of locomotion, but temporary 

 processes called pseudopodia. 



Mastigophora are more or less of definite form, and have one 

 or more permanent organs for locomotion or food capture in the 

 form of fiagella in the adult. 



Sporozoa are internal parasitic protozoa which have no organs 

 of locomotion or for the capture or digestion of food. They 

 reproduce only by some means of sporulation. 



Infusoria are provided with cilia for locomotary purposes. 



CLASS I. SARCODINA. 



Although Amoeba is specially referred to here it is only in its 

 resting stage that the typical body form is realised, as Sarcodina 

 are typically simple spherical bodies, such as the Eadiolaria and 

 Heliozoa, which float freely on the surface of water and have 

 pseudopodia radiating from them in all directions. But in the 

 Mycetozoa — semi-terrestrial protozoal masses which live on rotten 

 tree-trunks, fungi, &o. — the protoplasm forms large creeping 

 masses called plasmodia, — the latter including the well-known 

 parasitic disease of Cruciferous plants, " finger-and-Toe," pro- 

 duced by Plasmodiopliora Jn'ossicce of Woronin. 



These Sarcodina are divided into five sub-classes, the Amoebeea 

 (fig. 2), the Foraminifera (fig. 3), the Mycetozoa, the Eadiolaria, 

 and the Heliozoa. 



We need only refer to the first here. 



B 



