40 PROTOZOOLOGY 



cases, a special clathrate shell composed of silica, is to be found. 

 In some Radiolaria, isolated siliceous spicules occur as in Helio- 

 zoa, while in others the lateral development of the spines results 

 in production of highly complex and most beautiful shells with 

 various ornamentations or incorporation of foreign material. 

 Many pelagic radiolarians possess numerous conspicuous radiat- 

 ing spines in connection with the skeleton, which apparently aid 

 the organisms to maintain their existence in the open sea. 



Some flagellates may be encased in a chitinous lorica or house 

 and in addition there is occasionally a collar developed at one 

 end. The lorica found in the Ciliophora is mostly composed of 

 chitinous substance alone, especially in Peritricha, although some 

 produce a house made up of gelatinous secretion containing 

 foreign material as in Stentor (p. 581). In the Tintinnidiidae, the 

 loricae are either solely chitinous in numerous marine forms not 

 mentioned in the present work or composed of sand-grains or 

 coccoliths cemented together by chitinous secretion. 



Locomotor organellae 



Closely associated with the body surface are the organellae 

 of locomotion: pseudopodia, flagella, and cilia. These organellae 

 are not confined to Protozoa alone and occur in various cells of 

 Metazoa. All protoplasmic masses are capable of movement 

 which may result in change of their forms. 



Pseudopodia. A pseudopodium is a temporary projection of 

 part of the cytoplasm of those protozoans which do not possess 

 a definite pellicle. Pseudopodia are therefore a characteristic 

 organella of Sarcodina, though many Mastigophora and certain 

 Sporozoa, which lack a pellicle, are able also to produce them. 

 According to their form and structure, four kinds of pseudopodia 

 are distinguished. 



1). The lobopodium is formed by an extension of the ecto- 

 plasm and by a flow of endoplasm as is commonly found in 

 Amoeba proteus (Figs. 42; 140). It is finger- or tongue-like, some- 

 times 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, 



