182 



PROTOZOA. 



ever, be broad, lobed, or linger-like processes by means of which a 

 quick and flowing motion can be imparted to the body mass. A 

 tougher, clear homogeneous external layer (Exoplasm] is usually to 

 be distinguished as the peripheral boundary from a more fluid and 

 more granular internal mass (JEndoplasm). During motion the 

 former is projected in processes into which the granules of the latter 

 stream more or less quickly. 



In the stiffer pseudopodia streams of granules are observable, slow 

 but regular, passing from the base to the extremity and vice versa. 

 The explanation of these movements is to be sought in the contractility 

 of the surrounding portions of sarcode (fig. 120). 



A pulsating space, the contractile vacuole, is not unfreqently to be 

 found in the sarcode, e.g., Difflugia, Actinoplirys, Arcella (fig. 121). 

 Nuclei are also usually present in the sarcode, by which the morpho- 

 logical value of the Rhizopod body as cell or as cell aggregate is 



placed beyond all doubt. There are 

 also forms in the protoplasm of 

 which no trace of a cell nucleus has 

 been found. In such either the 

 protoplasm of the nucleus is not yet 

 differentiated as a separate structure 

 (the Monera of E. Haeckel), or we 

 have to do with a transient, non- 

 nucleated stage in the life-history. 

 The sarcode visually secretes sili- 

 cious or calcareous structures, either 

 as fine spicula and hollow spines 

 which are directed from the centre 

 to the periphery in regular order 

 and number, or as lattice-work 

 chambers (Badiolaria), which often 

 bear points and spines, or finally 



as single and many chambered shells with finely perforated walls 

 (Foraminifera) and one larger opening. Through this last (fig. 

 123), as well as through the countless pores of the small shells (fig. 

 122), the slender threads of sarcode pass out to the exterior as 

 pseudopodia, changing without intermission in form, size, and 

 number, and often joining themselves together in delicate networks 

 (figs. 122, 123). 



The pseudopodia, by their slow, creeping movements, afford a means 

 of locomotion, while they also serve for the taking up of nourishment 



FIG. 121. Amosla (Dactylosphcfm) poly- 

 podia (after Fr. E. Schultze). N, Nu- 

 cleus. Po. pulsating vacuole. 



