240 



PRACTICAL ZOOLOGY 



specialized kind of protoplasm; it is sometimes called nucleo- 

 plasm to distinguish it from the rest of the protoplasm, which 

 is designated cytoplasm. 



PROTOPLASM THE PHYSICAL BASIS OF LIFE. Protoplasm is 

 known as the physical basis of life since every organism, whether 



773 



as 



FIG. 139. Diagram of a typical cell. 



as, astrosphere; e, centre-some; ch, chromatin; cr, chromidia; ec, ecto- 

 plasm ; en, entoderm ; k, karyosome ; 1, linin ; m, mitochondria ; me, meta- 

 plasm; nm, nuclear membrane; p, plastid; pi, plasmosome or nucleolus; 

 s, cytoplasm ; v, vacuole. 



plant or animal, has this substance as a basis. We should there- 

 fore know something more about it. Ameba (Fig. 133) consists 

 of naked protoplasm. The outer layer is very clear, and rather 

 firm like stiff jelly; the inner mass is granular and more watery. 

 The activities of Ameba are those of animals in general, but in 

 the Metazoa these activities are distributed among many cells, a 

 condition known as division of labor among cells or specializa- 

 tion. 



