SYSTEMATIC SURVEY. 



105 



life history is complex. It appears as (a) an encysted form ; (b) a free- 

 swimming colony of ciliated cells (like the embryos of some sponges) ; 

 (<:) as ciliated units produced by the breaking up of (b) ; and (d) as 

 amoeboid forms resulting from the modification of the active units. 



(4) The Labyrinthulidea are represented by forms like Labyrinthnla 

 on Algae, 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 (Actinosph&riiun, 



FIG. 47. Formation of shell in a simple Foraminifer. 

 After Dreyer. 



In A the shell has one chamber ; B, C, and I) show the formation 

 of a second. Note outflowing pseudopodia and the enclosure of 

 the shell by a thin layer of protoplasm ; note also the nucleus 

 in the central protoplasm. 



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. 



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 



