MORPHOLOGY AND PHYSIOLOGY 25 



may be composed of characteristic plates, as in Coleps (Fig. 

 148). The pellicle, in many cases, may thicken locally and pro- 

 duce spinous projections or hooks which serve as protective or 

 attaching cell-organs. Gelatinous substances are sometimes 

 secreted by Protozoa for protection of the body. 



Some Protozoa secrete a test, or lorica, which encases the 

 protoplasmic body. The test may be composed of chitin, pseu- 

 dochitin, silicious or calcareous substances. An example of this 

 is the homogeneous chitinous shell of Arcella (Fig. 4). In others 

 the test is made up of scales produced in the cytoplasm and ce- 

 mented together around the body; and again the shell is formed 

 by cementing together foreign materials such as sand grains, 

 sponge skeletons, diatom shells and others. Various Foraminif- 

 era seem to possess a remarkable selective power in the use of 

 foreign materials for the construction of their tests. According 

 to Cushman, Psammosphaera fusca uses sand grains of uniform 

 color but of different sizes, while P. parva uses grains of more or 

 less uniform size but adds, as a rule, a single large acerose sponge 

 spicule, which is built into the test and which extends out both 

 ways considerably. Cushman thinks that this is not accidental, 

 since the specimens without the spicules are few and those with 

 a short or broken spicule are not found. P. howmanni, on the 

 other hand, uses only mica flakes which are found in a compara- 

 tively small amount, and P. rustica uses acerose sponge spicules 

 for the framework of the test, skilfully fitting smaller broken 

 pieces into polygonal areas. 



Closely associated with the body surface are the cell-organs 

 of locomotion, the pseudopodia, flagella and cilia. Pseudopodia 

 are usually temporary or semi-permanent cytoplasmic pro- 

 jections which serve for locomotion and food-capturing. Accord- 

 ing to their form and structure, four types are distinguishable: 



Lobopodia. These are temporary cytoplasmic projections 

 ordinarily composed of both ectoplasm and endoplasm, as in 

 Amoeba proteiis (Fig. 80). They are more or less broad with 

 rounded ends. 



Filopodia. These are also temporary cytoplasmic projections, 

 but are usually made up of the hyaline ectoplasm only. They 

 are more or less rod-like or filamentous, as in several Testacea 

 (Fig. 93). 



