32 



THE PROTOZOA 



form of cuticular productions or envelopes of various kinds, or 

 internal, in the form of an axis or framework. Both these types 

 of form-determining or skeletal elements, as they may be termed 

 broadly, may be present together in a given organism. 



1. Cuticular and Exoskeletal Structures. In the Sarcodina gener- 

 ally, and in a few examples of the Mastigophora and Sporozoa, the 

 body-protoplasm is quite naked at the surface, as already stated, 

 and not covered by any cuticle or firm covering. With these 

 exceptions, the bodies of Protozoa are clothed by a firm cortical 



oes 



G.U 



Fid. 14. Prorodon. tere. N, Macronucteus ; n, micronuoleus ; o, mouth ; <xs., 

 oesophagus surrounded by rod-apparatus (p. 433) ; /.., food vacuoles ; c.v., 

 contractile vacuole surrounded by feeding- vacuoles ; al., alveolar layer ; 

 at, meridional rows of cilia ; a., anal pore. After Schewiakoff, magnified 660 

 diameters. 



layer, which is produced either as a differentiation of, or secretion 

 by, the most superficial layer of the protoplasmic body, and which 

 receives various names in different cases. 



The very first beginnings of a cortical layer are seen in some 

 species of amoebae, such as Amoeba verrucosa species in which the 

 protoplasm, extremely viscid and slow-flowing, forms a delicate 

 investing pellicle at the surface. In these cases the pellicle is so 

 thin that it does not hinder the amoeboid movement appreciably 

 (Fig. 23). A further advance is seen in some of the Flagellata, 



