THE PHENOMENA OF LIFE. 9 



some other way producing) two or more parts, each of which is capable 

 of independent existence. The new amoebae manifest the same proper- 

 ties as their parent, perform the same functions, grow and reproduce in 

 their turn. This cycle of life is being continually passed through. 



In more complicated structures than the amoeba, the life of indi- 

 vidual protoplasmic cells is probably very short in comparison with that 

 of the organism they compose; and their constant decay and death 

 necessitate constant reproduction. 



The mode in which this takes place has long been the subject of 

 great controversy. 



It is now very generally believed that every cell is descended from 

 some pre-existing (mother-) cell. This derivation of cells from cells 



Fig. 7. Diagram of an ovum (a) undergoing segmentation-In (6) it has divided into two, in 

 Cc) into four; and in (d) the process has ended in the production of the so called "mulberry mass " 

 CFrey.) 



takes place by (1) gemmation, which essentially consists in the budding 

 off and separation of a portion of the parent cell; or (2) fission or divi- 

 sion. 



The exact manner of the division of cells is a matter of some diffi- 

 culty, and will not be described until the subject of the structure of 

 protoplasmic cells has been considered. 



Structure of Protoplasmic Cells. 



Protoplasm was formerly thought to be homogeneous: though this 

 may be true in some cases, it is now generally found to consist of two 

 substances, spongioplasm and hyaloplasm. The spongioplasm or reticii- 

 him forms a fine network, increases in relative amount as the cell grows 

 older, and has an affinity for staining reagents. The hyaloplasm is less 

 refractile, elastic, or extensile, and has no affinity for stains; it pre- 

 dominates in young cells, is thought to be fluid, and fills the interspaces 

 of the reticulum. The nodal points of the reticulum, with the grannies 

 (microsomes) found in the protoplasm, cause the granular appearance. 

 Butschli has recently asserted that protoplasm is an emulsion made up 

 of numerous microscopic vacuoles whose walls are in close apposition and 

 are seen under the microscope in optical section only, thus causing the 

 reticular appearance. This idea is accepted by few. 



The arrangement of the reticulum varies considerably in different 

 cells, and even in different parts of the same cell. Sometimes, for ex- 

 ample (fig. 8), the meshwork has an elongated radial arrangement from 



