n] MITOCHONDRIA, GOLGI APPARATUS 23 



by special methods. They have been observed, however, 

 in the living cell. About their nature and function there 

 has been much dispute. Some investigators maintain that 

 they are permanent cell organs, and that every mitochon- 

 drial body arises only from a pre-existing one, and writers 

 of this school have supposed that they play a great part in 

 the transmission of hereditary characters. Others consider 

 that they are comparatively transient structures, coming 

 into existence under special metabolic conditions of the cell, 

 as for example when it is building up or secreting some 

 product of protoplasmic activity such as yolk or skeletal 

 spicules, or when the cell is being rapidly metamorphosed 

 as in the change of a primitive germ-cell into a spermato- 

 zoon. In the present state of our knowledge this latter 

 opinion seems on the whole the more probable, but the sub- 

 ject is still very far from being settled. And the fact that 

 mitochondria, like the "Golgi bodies," next to be mentioned, 

 have the power of division, and possibly never come into 

 existence except from a pre-existing body of the same kind, 

 certainly supports the opinion held by some cytologists, 

 that 'they are permanent cell-organs in some ways com- 

 parable to the plastids (chloroplasts, etc.) of plant cells. 



Another constituent of the cytoplasm which recent work 

 has shown quite possibly to exist in all cells, and which is 

 certainly present in cells of very varied types from animals 

 of many groups, is the so-called "internal reticular appara- 

 tus" of GOLGI, often known shortly as the Golgi apparatus. 

 This was first observed in nerve-cells, but more recent in- 

 vestigation has shown that it is so wide-spread that it is 

 quite probably a constant cell-constituent. It is, however, 

 comparatively little known, from the fact that it is invisible 

 in the fresh cell and stains only by very special methods, 

 the chief of which is Golgi's silver impregnation method ; it 



