388 GREAT STEPS IN ORGANIC EVOLUTION 



was formed an enveloping matrix of restless semifluid sub- 

 stance, rapidly discharging what explosives it got a hold of, 

 in other words living nearly up to its income, and exhibit- 

 ing streaming outflowings and amoeboid movements. This 

 ivas the first animal, and it preyed on smaller organisms. 

 When the chromatin granules concentrated into and were in- 

 tegrated into a definite nucleus — an organised kernel — the 

 first true cell was formed. The details are all uncertain, but 

 it is probably safe to say that a long journey had to be trav- 

 elled before even the first cell appeared. It need hardly be 

 said that the numerous suppositions made in this paragraph 

 have a factual basis in existing organisms of low degree. 



§ 3. Establishment of Diverse Types of Cellular 



Organisation. 



The next great series of steps had to do with the estab- 

 lishment of a variety of types of cellular organisation, besides 

 the bacterial and amoeboid already referred to. Some active 

 forms evolved cilia and flagella ; some sluggish forms evolved 

 protective cysts, adapted to unpropitious circumstances and 

 times ; some creeping forms got a skeleton which made them 

 more coherent; others were adapted to flotation ; and so on end- 

 lessly. A luminous idea was long ago developed by Prof. 

 Patrick Geddes in his conception of the ^ cell-cycle ', that there 

 are three great pathways of cellular evolution — the very act- 

 ive Infusorian-line, the very sluggish Sporozoon-line, and the 

 median compromise of the Amoeboid-line. These three lines 

 correspond to the three physiological regimes of lavish ex- 

 penditure or ^ living dangerously \ of preponderant saving 

 or a life of ease, and of a balance between these extremes. 

 The cells of higher animals may be in part classified on 

 these three lines — ciliated, encysted, amoeboid ; and there is 



