THE ORIGIN OF THE ANIMAL KINGDOM. 6 1 



of nucleus. In many cases, however, especially 

 among animals, the independent bits of protoplasm 

 were found to have no wall to surround them, and 

 many cells were found in which no nucleus could be 

 demonstrated. Still they were seen plainly to be 



FIG. 2. A cell./' Protoplasm. N Nucleus. Ne Nucleolus. Civ Cell wall. 



independent units and surely to deserve the name of 

 cells. Thus the term cell came to mean any inde- 

 pendent mass of protoplasm, with or without a 

 nucleus, with or without a cell wall. More recently 

 however, it has been quite definitely shown that, 

 though the cell wall is not always present, and there- 

 fore is not necessary to the constitution of a cell, the 

 nucleus is probably always present in active cells, 

 either as a distinct body or as a diffused mass. A 

 cell thus becomes an independent bit of protoplasm 

 with a nucleus ; or better, perhaps, since recent study 

 shows the fundamental importance of the nucleus, a 

 bit of nuclear matter with surrounding protoplasm. 



