56 



ZOOLOGY 



SECT. 



as far as the nucleus. Living organisms are devoured in much 

 the same way as in Amceba: each is ingested along with a 

 droplet of water, and is thus seen, during digestion, to lie in a 

 definite cavity of the protoplasm, called a food-vacuolc. 



Actinosphcerium (Fig. 38, A), another fresh-water form, is more 

 complex. The protoplasm is distinctly divided into a central mass, 

 the medulla or endosarc (B, mcd.), in which the vacuoles are small, 

 and an outer layer, the cortex or ectosarc (cort.), in which they are 



N 



PIG. 38. Actinosphserium eichhornii. A, the entire organism ; B, a small portion 

 highly magnified ; (/</. chromatopliore ; cort. cortex ; c. rac. contractile vacuole ; med. medulla ; 

 nu. nuclei. (From Biitschli's Protozoa, after Hertwig and Lesser.) 



very large. There are numerous nuclei (nu.) and chromatophores 

 (chr.), the latter coloured green by chlorophyll. 



Many genera form colonies. Numerous zooids may be united 

 by bridges of protoplasm into an open network, or the connecting 

 bridges may be shorter and the zooids more numerous, giving the 

 colony a more compact appearance. 



Transitional stages occur between the naked genera already re- 

 ferred to and forms with a distinct skeleton. Sometimes the body 

 simply surrounds itself with a temporary gelatinous investment 

 (Fig. 39, 2, g.), in other cases it is surrounded by a capsule of loosely 

 woven fibres through which the pseudopods pass, thus reminding 

 us of the state of things characteristic of perforate Foraminifera. 



