SYSTEMATIC SURVEY. 



99 



(c ) as ciliated units produced by the breaking up of (6) ; and [d) as 

 amoeboid forms resulting from the modification of the active units. 



(4) The Labyrinthulidea are represented by forms like Labyrinthida 

 on AlgEe, and Chlamydomyxa on bog-moss, which consist of a mass of 

 protoplasm spread out into a network, and of numerous spindle-shaped 

 units, which travel continually up and down the threads of the living 

 net. 



As (5) Heliozoa are classified the sun-animalcules {Actinospharium, 

 Actinophrys sol), and others, in which there are stiff processes radiating 

 from a spherical body. Reproduction may be by division or by spore 

 formation ; skeletal structures may be represented by spicules. 



Fig. 44.- 



-A Foraminifer (Polystomel/a) showing shell and pseudopodia. 

 — After Schultze. 



The (6) Foraminifera or Reticularia include an interesting series 

 of shelled forms in which the peripheral protoplasm forms a mass of 

 interlacing threads. Most are marine, the shell is usually calcareous, 

 more rarely arenaceous or chitinous, and encloses the central mass only. 

 Foraminifera are common as fossils from Silurian rocks onwards, and 

 at the present day are very important in the formation of calcareous 

 ooze ; in this respect Globigerina, with a chambered shell, is especially 

 important ; others are Gromia, found in both fresh and salt water ; 

 Haliphysema, a form utilising sponge-spicules to cover itself, once 

 mistaken for a minute sponge, or for a very simple many -celled 

 animal. 



Most kinds of chalk consist mainly of the shells of Foraminifera 



