Ixviii THE BEGINNINGS OF LIFE. 



but in other cases (^) they become converted into mother- 

 cells by their contents undergoing a process of quaternary 

 subdivision, which repeats itself again and again. This pro- 

 perty of repeated and incessant subdivision is thus seen to be 

 common both to the Lichen and to the Moss-gonidium, and, 

 as Dr. Hicks points out, the process is commenced so early 

 in the cell ' that one subdivision is hardly fairly perceptible 

 before the next can be recognized ; indeed, in some of the 

 cells three or four generations are included in one parent.' 

 The result of this process in either case may be the produc- 

 tion of segmental divisions, 'so small as scarcely to show 

 any distinction between cell-wall and contents;' which, 

 however, 'gradually increase in size, so as at last to equal 

 the original parent cell.' Not only were the products of 

 this subdivision incapable of being discriminated micro- 

 scopically from those of the Lichen gonidia, but they even 

 resembled them also in their tendency to keep on for an 

 indefinite time in that particular mode of growth and repro- 

 duction with which they had commenced. Dr. Hicks says : — 

 ' This can readily be observed by any one who will take 

 the trouble. Large areas may thus be covered by the growth 

 of these cells, which may continue for a long period of time, 

 certainly over a year, and probably, as far as I can make 

 out, for many years. ... It may always be noticed on the 

 face of any wall where Mosses grow, that underneath each 

 patch a large stream of these Chlorococcus-like bodies may 

 be seen, running downwards.' 



4. Sometimes, however, instead of the production of the 

 globular cells from the ends of the filaments, the whole of 

 the cells of a tapering filament may undergo this quaternary 

 form of segmentation in situ. The cell-walls become thicker 

 and the filament broader, whilst segmentation goes on. After 

 a time the parent cell-walls dissolve away, and the Chloro- 

 coccus-like bodies are liberated. This mode of growth has 



