40 



BIOLOGY OF THE PROTOZOA 



is the external zone of protoplasm which, as the surface of contact 

 between the organism and the outer workl, has become modified 

 in various ways. Such outer differentiations are usually transparent 

 so that the nature of the internal protoplasm may be made out in 

 more or less detail. This is particularly true of the so-called 

 "naked" forms such as Amoeba yroieiis, etc., in which the surface 

 protoplasm is only slightly different from the internal substance and 

 is made up of living material. Here the entire organism is living 





^ ^i 



' % 





\ %n 



Li 



Fig. 19.- 



-Hyalohryon defortnans Awerinz. Arboroid colony with external attach- 

 ment of individual cups. 



protoplasm which appears as a drop of fluid substance, grayish- 

 white in color, viscid in physical character bnt tenuous and with no 

 tendency to mix with the surrounding water. In such living cells, 

 internal movement of the protoplasm is manifested hy the streaming 

 (cyclosis) of distinct granules some of which are more refractile than 

 others, but which are present in all cells, and invariably character- 

 istic of the inner plasm. Spherical spaces or vacuoles, are also 

 visible in the living forms, sometimes with solid, usuall;\' foreign, 

 matter within them (gastric vacuoles, defecatory vacuoles), some- 



