THE MASTIGOPHORA 



113 



distinguished by the peculiar parenchymatous structure and by the 

 presence of a tentacle and a collar. 



A. Protoplasmic Structure 



The alveoli, forming the structural basis of the protoplasm, vary in 

 size from minute and scarcely visible spaces to large vacuoles. In 

 the majority of forms, they are arranged in a typical outer layer {Rin- 

 denschicht) of small-sized alveoli, surrounding an inner mass of larger 

 ones {e.g. Chilomonas). The protoplasm is not equally dense in all 



Fig. 59- — Proterospongia Hceckell S. K. [S. KENT.] 



cases, but, as in the Rhizopoda, may be of variable consistency. It 

 may be so soft and flexible that, as in Amceba, the periphery will give 

 way, and pseudopodia may be formed at any point in response to 

 local changes in the surface tension (Euglenoids and forms of Asta- 

 sia). There is but little tendency to the differentiation into zones, 

 so frequently seen in Rhizopoda, and only rarely is there a differen- 

 tiation into ectoplasm and endoplasm (Mastigamazba). 



Klebs ('92) distinguishes two types of peripheral structures, the 

 periplasts and outer coats, stalks being included with the latter. 

 The periplasts include all cuticular differentiations which are a living 



