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 



Fig. 139. — Diagram of a typical cell. 



as, astrosphere ; c, centrosome; 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. Amcba (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 Mclazoa these activities are distributed among many cells, a 

 condition known as division of labor among cells or specializa- 

 tion. 



