io8 PHLYUM PROTOZOA THE SIMPLEST ANIMALS. 



B. Predominantly amoeboid Protozoa. Rhizopoda. The 



simplest Rhizooods generally resemble Amoeba, and are ranked in the 

 class (3) Lobosa. They may reproduce simply by division, as does 

 Amoeba itself, or may liberate several buds at once (Arcelld), or form 

 spores which conjugate (Pelomyxa). Various forms, such as A reel la, 

 are furnished with a shell. 



(4) The Labyrinthulidea are represented by forms like Labyrinthula 

 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 



FlG. 49. Formation of shell in a simple Foraminifer. 

 After Dreyer. 



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

 of a second. Note outflowing psuedopodia and the enclosure of 

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

 in the central protoplasm. 



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. 



The (6) Foraminifera or Reticularia include an interesting series 

 of shelled forms in which the peripheral protoplasm forms branching 

 interlacing threads. A few simple forms occur in fresh water ; the great 

 majority occur on the floor of - the sea at varying depths ; some 



