10 General Morphology of the Protozoa 



covering applied directly to the surface of the body and is comparable to 

 the thick cell wall found in higher plants. The flagella emerge through 

 pores in the theca. A theca may be somewhat flexible, allowing slight 

 changes in form, or it may be rigid. The firmness imparted by cellulose 

 or pectins is sometimes increased by impregnation with inorganic salts 

 to produce a hard covering, as in Phacotus, Trachelomonas, and some of 

 the dinoflagellates. The theca of many dinoflagellates is differentiated into 

 a number of plates (Fig. 1. 5, A, B), the pattern varying with the species. 

 Lorica, test, and shell are terms applied to coverings which often fit 

 less closely than the theca and hence are less comparable to the typical 

 cell wall of plants. A lorica (Fig. 1. 5, C, D) is usually a tubular or vase- 

 like structure with an opening through which the anterior part of the 



^v 











A 









B 



^r^' 



Fig. 1. 6. Groups of myxopodia (A) and axopodia (B); diagrammatic. 



body or its appendages can be extended. The base of the lorica, in sessile 

 species, may be attached directly to the substratum or may end in a 

 stalk. In colonial types (Fig. 1. 3, C, D), one lorica may be attached to 

 another directly or by means of a stalk. A lorica may be composed en- 

 tirely of secreted material or may be reinforced with diatom shells, sand 

 grains, or other foreign particles. 



The tests (or shells) of many Sarcodina vary widely in form and com- 

 position. Some appear to be homogeneous. Others consist mainly of sep- 

 arate elements cemented together, as in Euglypha and Difflugia (Fig. 1. 

 5, E, F). The test of Euglypha is composed of plates, formed within the 

 body prior to fission; that of Difflugia is made of sand grains embedded 

 in a secreted cement. The comparable arenaceous tests of certain Foram- 

 iniferida (Chapter V) are built of sand grains, discarded tests, sponge 



