458 BIOLOGY OF THE PROTOZOA 



in a swarm of minute naked amebae. These develop into an adult 

 form of different type which may likewise undergo plasmotomy 

 leading to the formation of gamonts and gametes. The latter, upon 

 fertilization, give rise to the initial type of organism. In this cycle, 

 the original asexual generation differs from the later sexual genera- 

 tion by the presence of a peculiar type of test consisting of radially- 

 arranged spicules of magnesium carbonate. 



The forms included in this Order fall naturally into two families— 

 Arcellidae and Euglyphidae (see Key for genera). 



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Fig. 189. — Chlamydophrys utercorea. (From Doflein after Schaudinn.) 



Family 1. Arcellidae.— Tests transparent or opaque by reason of 

 covering of foreign bodies picked up by the protoplasm and deposited 

 on the outside where they are cemented to the chitinous membrane. 



Structure and materials of the shell afford a basis for further 

 classification of the family. They are either pyriform or shaped 

 like a watch-glass; the membrane may be rigid or flexible and the 

 aperture central or asymmetrically placed. 



Family 2. Euglyphidae. — In members of this family the test is 

 covered by silicious plates or scales and the pseudopodia are of a 

 filose, branching type. The tests may be either symmetrical or 



