MORPHOLOGY 41 



Vahlkampfia Umax, Pyxidicula operculata, etc., in which case it 

 is a broadly tongue-like extension of the body in one direction 

 and the progressive movement of the organisms is comparatively 

 rapid. The lobopodia may occasionally be conical in general 

 shape, as in Amoeba spumosa. Although ordinarily the formation 

 of lobopodia is by general flow of the cytoplasm, in some it is 

 sudden and "eruptive," as in Endamoeha hlattae or Entamoeba 

 histolytica in which the flow of the endoplasm presses against 

 the inner zone of the ectoplasm and the accumulated pressure 

 finally causes breaks through the line, resulting in a sudden ex- 

 tension of the endoplasmic flow at that point. 



2). The filopodium is a more or less filamentous projection com- 

 posed almost exclusively of the ectoplasm. It may sometimes be 

 branched, but the branches do not anastomose. Many testaceans, 

 such as Lecythium, Boderia, Plagiophrys, Pamphagus, Euglypha, 

 etc., form this type of pseudopodia. The pseudopodia of Aynoeba 

 radiosa may be considered as approaching this type more than 

 the lobopodia. 



3). The rhizopodium is also filamentous, but branching and 

 anastomosing. It is found in numerous Foraminifera, such as 

 Elphidium, Peneroplis (Fig. 5), etc., and in certain testaceans, 

 such as Lieberkuhnia, Myxotheca, etc. The abundantly branch- 

 ing and anastomosing rhizopodia often produce a large network 

 which serve almost exclusively for capturing prey. 



4). The axopodium is, unlike the other three types, a more or 

 less semi-permanent structure and composed of axial rod and 

 cytoplasmic envelope. The axopodia are found in many Heliozoa, 

 such as Actinophrys, Actinosphaerium, Camptonema, Sphaera- 

 strum, and Acanthocystis. The axial rod, which is composed of 

 fibrils (Doflein; Roskin), arises from the central body or the 

 nucleus located in the approximate center of the body, from each 

 of the nuclei in multinucleate forms, or from the zone between 

 the ectoplasm and endoplasm (Fig. 6). Although semipermanent 

 in structure, the axial rod is easily absorbed and reformed. In the 

 genera of Heliozoa, not mentioned above and in numerous radio- 

 larians, the radiating filamentous pseudopodia are so extremely 

 delicate that it is difficult to determine whether an axial rod exists 

 in each or not, although they resemble axopodia in general ap- 

 pearance. 



There is no sharp demarcation between the four types of 



