The Sarcodina 237 



(Fig. 5. 24, N-P) and therefore should be transferred to the genus 

 Naegleria. 



Family 2. Amoebidae. These are the free-living amoebae which lack a 

 flagellate phase. Although complex cycles involving polymorphism and 

 syngamy have been described, such interpretations apparently were based 

 on cultures contaminated with other species of Amoebidae, Mycetozoa, 

 and water-molds (67). At present, it appears that the life-cycle is limited 

 to the amoeboid stage and a cyst. 



Classification of the Amoebidae is not yet on a satisfactory basis and 

 there remains a certain amount of disagreement concerning the genera 

 which should be recognized. Furthermore, the concept of a single family 

 for all the free-living amoebae is subject to the objection that habitat is 

 not necessarily an accurate gauge of zoological relationships. Conse- 

 quently, there is at least a reasonable basis for various suggestions that 

 the group should be split into less heterogeneous families. In a sense, 

 problems of taxonomy are complicated by the very simplicity of amoebae. 

 Lack of the more obvious fixed characteristics typical of many other 

 groups necessarily limits the taxonomist to consideration of range in size, 

 form of the body, type of pseudopodia, methods of locomotion, structure 

 of the nucleus, and the form and nature of cytoplasmic inclusions. Aside 

 from the nuclear picture, which should show reasonable constancy, these 

 characteristics vary within greater or lesser limits and presumably are 

 subject to significant environmental influences. The effective utilization 

 of such dynamic traits in taxonomy obviously demands extensive knowl- 

 edge of amoebae, particularly as living organisms. Consequently, there is 

 much need for the detailed study of many species which are not yet 

 thoroughly characterized. In some cases, adequate characterization may 

 depend upon pure-line cultures for determining the range in form and 

 behavior to be expected of jiarticular species. The systematic investiga- 

 tion of nuclear structure and division, on the order of some recent work 

 with Naegleria (113), also should yield information of taxonomic value. 

 For instance, a nucleus with a large endosome is characteristic of both 

 Vnhlkampfia (24) and Acanthamoeha (150), but the mitotic pictures are 

 strikingly different, the endosome being resorbed in the latter. 



It has been pointed out very clearly (132) that amoebae differ char- 

 acteristically (Fig. 5. 25) with respect to types of pseudopodia, methods 

 of locomotion, form of the body and the nature of its changes in form, 

 presence or absence of a "uroid" (a gioup of thin cytoplasmic projections 

 at the posterior end), form of the nucleus, and even the types of cyto- 

 plasmic crystals in certain large fresh-water species. Some amoebae, for 

 example, form determinate pseudopodia which grow to a more or less 

 definite size and are then withdrawn, never becoming large enough to 

 include the entire amoeba and thus not directing locomotion. Others 

 develop indeterminate pseudopodia which are not restricted in size and 



