42 PROTOZOOLOGY 



Sarcodina, though many Mastigophora and certain Sporozoa, which 

 lack a pellicle, are also able to produce them. According to their 

 form and structure, four kinds of pseudopodia are distinguished. 



1). Lobopodium is formed by an extension of the ectoplasm, 

 accompanied by a flow of endoplasm as is commonly found in 

 Amoeba proteus (Figs. 44; 161). It is finger- or tongue-like, sometimes 

 branched, and its distal end is typically rounded. It is quickly 

 formed and equally quickly retracted. In many cases, there are 

 many pseudopodia formed from the entire body surface, in which 

 the largest one will counteract the smaller ones and the organism 

 will move in one direction; while in others, there may be a single 

 pseudopodium formed, as in Amoeba striata, A. guttula, Vahlkampfia 

 Umax, Pelomyxa caroUnensis, 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 a general flow 

 of the cytoplasm, in some it is sudden and "eruptive," as in End- 

 amoeba blattae or Entamoeba histolytica in which the flow of the endo- 

 plasm presses against the inner zone of the ectoplasm and the ac- 

 cumulated pressure finally causes breaks through the zone, resulting 

 in a sudden extension of the endoplasmic flow at that point. 



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

 posed almost exclusively of the ectoplasm. It may be sometimes 

 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 Amoeba 

 radiosa may be considered as approaching this type rather than the 

 lobopodia. 



3). 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 Lieberkiihnia, Myxotheca, etc. The abundantly branching and 

 anastomosing rhizopodia often produce a large network which serve 

 almost exclusively for capturing prey. 



4). Axopodium is, unlike the other three types, a more or less 

 semi-permanent structure and composed of axial rod and cytoplas- 

 mic envelope. Axopodia are found in many Heliozoa, such as Actino- 

 phrys, Actinosphaerium, Camptonema, Sphaerastrum, and Acan- 

 thocystis. 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 multi- 



