244 The Sarcodina 



Life-histories. Fission in Testacida typically involves retention of the 

 old test by one daughter organism. As traced in living Nebela collaris 

 (87), stored sand grains are passed into the lower part of the cytoplasm 

 which is protruded from the mouth of the test at the beginning of fission. 

 This naked portion gradually assumes the form of an adult and then de- 

 velops a new test. Nuclear .division occurs next and is followed by fission 

 and separation of the two organisms. In the Euglyphidae, reserve shell 



Fig 5 30 A. Cyst of Heleopera picta Leidy, test closed by operculum, 

 organism within cyst membrane; x250 (after L.). B. Cyst of Triuema 

 eruhelys. cyst membrane, "cyst-shell," and original test (mouth plugged 

 with debris); xll90 (after Volz). C. Encapsulated, or "drought-stage." m 

 Eughpha laevis, as found on dry moss; shell closed by a secreted membrane 

 (mouth of test sometimes plugged with debris); x800 (after Volz). D-H. 

 "Association" in Nebela collaris, from living (after MacKinlay). 



plates appear in the cytoplasm, are stored in the perinuclear region, and 

 are used later for construction of the new test in fission. 



Binary fission may not be the only method of reproduction. Occasional 

 production of a number of small amoebulae has been reported in Dij- 

 flugia (42), Centropyxis (20), and Arcella (21, 64). Perhaps this phenom- 

 enon is to be correlated with the reported occurrence of multinucleate 

 stages in Arcella (107). These small amoebae may undergo fission, but 

 they increase in size sooner or later and secrete a normal test. The ob- 

 servations of Cavallini (20, 21) were based on clone cultures. Although 



