276 Viiiversitij vf California PHblications in Zoologij [Vol. 10 



Should the two species of Dimastigamoeha prove to have a life- 

 history comparable to that of Naegleria, then Dimastigamoeha would 

 be applicable, and not until then. 



Other forms which should be added to the above list are the "kul- 

 turamoben" of Wasielewsky and liirsehfeld (1910). the limax amoeba 

 described by AVherry (1018), and possibly Amoeba tachnpodia Glaser 

 (1912a). ■] 



F. SUMMARY 



1. Pure mixed cultures of a soil amoeba, Naegleria gruberi, have 

 been maintained under laboratory conditions during two years. In 

 these cultures ency.stment and exeystment, enflagellation and exfiagel- 

 lation. exogenous and endogenous budding occur. 



2. In division by binary fi.ssion, which is promitotie, the spindle is 

 within the nuclear membrane. It has two large chromatic polar ma.sses 

 of karyosomie origin with polar caps of plastin more or less evident. 

 The spindle fibers are formed in the angle of the dividing dumb-bell 

 shaped chromatic karyosome. Tliey come from the peripheral and 

 karyosomie plastin. The eight subequal chromosomes come from the 

 peripheral chromatin with an addition from that of the karyo.some. 

 They are formed in a regular equatorial plate and later are divided 

 by constriction. 



3. The nucleus. is reconstructed as follows : the karyosome is formed 

 from the chromatic polar mass containing the centriole and from part 

 at least of the chromosomic ma.ss, while its plastin center comes from 

 the centrodesraose and the remains of the spindle. The peripheral 

 chromatin and plastin emerge from the network between the chromatic 

 polar mass and the chromosome mass. Stages of nuclear reconstruc- 

 tion simulate amitosis and have been so interpreted by Hogue (1914) 

 and others. No cases of true amitosis have been fovmd. 



4. Evidence of multiple fission, which is apparently rare, was found 

 in amoebas containing two and three spindles. 



5. Under conditions which have not been determined, exogenous 

 budding occurs in which peripheral lobes of cytoplasm are constricted 

 ofl', each containing chromidia given off from the nucleus. These 

 chromidia then reorganize to form nuclei of the new small individuals 

 in w^hich later coincident growth of nucleus and cytopla.sm ensues. 



