I PROTOZOA 15 



Radiolaria, whose bodies are surrounded by a thick gelatinous envelope (ealymna), 

 filled with vacuoles and alveoles, the case is more complicated. The extra-capsular 

 protoplasm forms a layer on the exterior of the capsular membrane (Barcomatrix) 

 and, further, a network on the surface of the ealymna (sarcodyctium). From the 

 latter, which is connected with the former by intra-calymnary protoplasmic cords 

 and strands, the extra-oalymnary pseudopodia radiate. 



Flagella cannot be sharply distinguished from pseudopodia. They 

 are processes of the exoplasm (where such exists) which, in the 

 Flagellata and in early stages of the life of many other Protista, appear 

 at special points of the body in small numbers (one or two, rarely 

 more). 



Undulating membranes have also been observed in a few Flagellata. 

 Cilia are characteristic of the Infusoria and the young stage of the 

 Siidoria. These are fine vibratile processes of the ectoplasm, which 

 vary in length, strength, and shape ; they are arranged in different 

 characteristic ways in each division, either spreading over the whole 

 body or restricted to certain regions, and specially forming spirals about 

 the mouth, or belts. 



In the Cystoflagellata {Nodiluca), besides the ordinary flagellum at 

 the base of the oral aperture, there is • a large band-like flagellum 

 which moves slowly ; this is a protoplasmic outgrowth of complicated 

 structure (Fig. 11, p. 9, hg). 



In the Gregarina special organs of locomotion are wanting ; the 

 ectoplasm here appears peculiarly contractile, just as in the Infusoria, 

 where it is often diflferentiated into parallel contractile and non- 

 contractile strips (furrows and ribs). Another differentiation of 

 the ectoplasm is the so-called stalk musele of the Vorticella (Fig. 16, 

 p. 10), which in contracting rolls itself up spirally. Here belong also 

 the myophrises of the Acanthometridce — filamentous processes which can 

 contract suddenly, but not repeatedly, and which are arranged on the 

 sarcodyctium in a circle round each skeletal spine. It is supposed 

 that they perform hydrostatic functions. 



In the Sudoria are found variable processes, mostly terminated by 

 a knob, and used as suctorial tubes, which are closely connected with 

 pseudopodia. The contents of the body of the penetrated Infusorian 

 or Alg flows through the suctorial tube into the body of the Acinetan. 



III. Membranes, Shells, Skeletal Formations. 



These are extraordinarily numerous. Many Protista, Amaha, and 

 Flagellata are naked. In simple cases the protoplasm secretes at the 

 surface a chitinous membrane (Gromia), which may be composed of 

 small plates (Arcella). Occasionally small foreign particles are united, 

 by a binding medium supplied by the body, into a sort of' case 

 (Difflugia). A fine cuticle is found in most Infusoria ; in some cases 

 this may harden into shells or carapaces. A cuticle (cell-integu- 

 ment) is further found in Gregarina and many Flagellata, and can 



