7i6 



PROTOZOA. 



Fig. 3. SIIBLLS OF FORAMINIFERA. 



A, Nummulites. 



B, Nonionina. 



C, Lagena. 



D, Globigerina. 



E, Milliola. 



such forms were long considered to be minute Molluscs. The shells of the 



Globigerina, or globe- bearers (D), help largely to build up Chalk. They are said 



to constitute almost one-third of the ooze 

 covering vast areas of the sea-bottom in 

 the North Atlantic. Milliolite shells (E) 

 are the chief constituent of the stone of 

 which the houses of Paris are built. 

 Nummilitic limestones cover an enormous 

 area of Central and Southern Europe, 

 North Africa, West Asia, and India. All 

 limestones indeed abound in the shells of 

 Foraminifera, some species being found 

 in the Coal formations also. 



The Foraminifera nearly all live in the 

 sea, creeping along its bottom ; but some 

 float about. Young ones are produced by 

 the breaking up of the protoplasm into 

 small portions, which secrete their charac- 

 teristic shelly covering before leaving the 

 body of the parent. Some young Fora- 

 minifera have very simple single^ shells, but others are provided from the first 



with a three-chambered shell. 



Passing from those Protozoa whose protoplasmic processes are mere 



protrusions of the soft body showing no definite shape, but constantly 



varying, we come to others in which these body processes are highly 



specialised, and here again we have naked and shelled forms. 



The Heliozoa, or Sun animalcules (Fig. 4), have straight, ray-like 



pseudopodia, which, however, are not rigid, but when brought in contact 



with particles of food, 

 The Heliozoa, can contract or bend so .. , 



as to draw them in to- \ \ : , / . / / 



wards the body. Sometimes a minute 



animalcule, touching one of the rays, appears 



to become paralysed and to glide down the 



pseudopodium to its root, where a protruding 



part of the protoplasm can draw in it. In 



most of the Heliozoa the body is naked, and 



the contractile vesicle is very conspicuous, 



often growing to a very large size at the 



edge of the body, and bursting with such 



violence as to shake the whole animal. 



Some idea of the size of these animalcules 



Can be gained from the fact that four hundred 



of them set closely side .by side would 



measure an inch. In spite of the formidable rays by which the Sun 



animalcule is surrounded, it often falls a prey to a simple Amoeba, which 



either envelops the whole animalcule or tears out portions of its soft body. 



Next in order above the Sun animalcules, and far more complicated in 



appearance on account of their elaborate skeletons, are 



The Kadiolaria. the Ray animalcules or Radiolaria. In these the soft 



body is not, as in the Foraminifera, enclosed in an almost 



continuous outer shell, but the hard matter, usually of a flinty nature, 



-' /'/i.V'rv 



Fig. 4. THE SUN ANIMALCULE 

 (Actinophrys sol). 



