March 28, 1913] 



SCIENCE 



495 



was studied during the past year under vary- 

 ing conditions of environment. The culture 

 contained the descendants of a single amcBba 

 grown in symbiosis with a single species of 

 bacillus. 



My work was started with the idea of in- 

 vestigating the physical and chemical condi- 

 tions necessary for the growth of this par- 

 ticular amoeba. When, in the course of the 

 work, it was discovered that the trophozoits 

 had the ability to turn, apparently at will, 

 into actively motile flagellated forms, my 

 efforts were directed mainly towards investi- 

 gating, first, the effects of varying environ- 

 ment upon the morphology and development 

 of the amceba and, second, the conditions 

 which led to the production of flagellated 

 forms. 



The trophozoits usually possess a single 

 nucleus with the large karyosome and thick 

 nuclear membrane characteristic of members 

 of the limas group. 



The flagellated forms vary in shape, but are 

 most often egg-shaped or pyriform, with the 

 nucleus situated at the pole, from which two 

 long, delicate flagella arise. 



These flagellates disappear instantly if a 

 thin cover-glass is placed on a preparation, 

 but may be watched for varying lengths of 

 time in a hanging drop. The metamorphosis 

 of one may be described briefly as follows: 

 For a while it maintained the elongated form; 

 then became pyriform, and whirled round and 

 round, and in a minute or so, during its 

 gyrations, it projected numerous waves of 

 blunt pseudopodia; shortly it became elon- 

 gated again. It progressed in this form until 

 twenty minutes after the observation com- 

 menced, when it suddenly became motionless 

 and spherical. In a few moments it projected 

 a clear blunt pseudopod into which the endo- 

 plasm flowed and then it wandered off as a 

 typical trophozoit of the limax type. 



Throughout a long series of cultural experi- 

 ments it was found that this metamorphosis 

 occurred very inconstantly. Traces of vari- 

 ous monovalent and bivalent salts seemed to 

 exert no beneficial effect. Daily observations 



on one subculture were made during more 

 than two months without revealing any flagel- 

 lated forms. However, it was finally discov- 

 ered that if the trophozoits were first grown 

 in hen's ovomucoid containing a trace of the 

 egg yolk, the development of the flagellated 

 forms was favored. Furthermore, that they 

 could be constantly obtained if the cultiva- 

 tions were carried out in hanging drops placed 

 in contact with an abundant supply of free 

 oxygen. 



The technique is as follows: a loopful from 

 the surface of a yolk-ovomucoid culture con- 

 taining the trophozoits is mixed with two or 

 three loopfuls of distilled water on a cover- 

 glass and placed on a Barber moist chamber 

 at 22°-25° C. Wo flagellates may be seen in 

 an hour or so, but hundreds may be seen 

 after three or four hours. 



Two "pure lines "—each originating from 

 a single flagellate — were obtained for me by 

 Dr. G. L. Kite, by means of the Barber isola- 

 tion pipette. Both of these showed a much 

 greater tendency to flagellate than the orig- 

 inal stock. 



Since the ability to turn over into a flagel- 

 lated stage has been established as a generic 

 character, a technique which will enable one 

 to determine this power is evidently of im- 

 portance. 



In 1912 Chatton and Lalung-Bonnaire es- 

 tablished the new genus VaJilkampfia (in 

 honor of E. Vahlkampf, who was the first to 

 make known the characteristic mitosis of these 

 amoebas) to include those members of the 

 limax group which had the ability to flagel- 

 late. These amoebse are said to be always 

 uninucleated. Nuclear division is by promi- 

 tosis. They multiply after nuclear division 

 by simple fission. Their cysts are always 

 uninucleate. 



My findings show that these generic char- 

 acters must be greatly extended. For ex- 

 ample, under certain cultural conditions the 

 trophozoits form endogenous buds; under 

 other conditions, characterized by a reduced 

 oxygen tension, the nucleus apparently divides 

 repeatedly by amitosis, without division of 



