IO 



EVOLUTION IN THE PAST 



From this point the development of animal life can be 

 more closely followed than that of plant life. Each cell having 

 to support itself, the cells in a ball-shaped colony must have 

 striven to occupy and retain a surface position so as to be in 

 contact with the outer world. As cell multiplication increased, 

 the struggle for outside accommodation must have become 

 intense, and the cells whose fate it was to lie inside must have 

 perished and polluted the colony unless an improved economy 

 could be effected. 



Then came the great effort to deal with this congested con- 

 dition, known in biology as the Mulberry stage (Morula). 

 The solution ultimately reached is probably represented by 

 the stage biologically known as the Blaiosphere or Bud-like 



Morula Stage. Blastophere (in section). 



(Highly magnified.) 



stage. Taking this as a guide, the inner cells, by some 

 unknown process, were forced up to the surface, and the 

 vacated interior became rilled with water. The colony had 

 now become a small ball-shaped mass overspread with a 

 single layer of cells. 



To what extent this outward-forcing process could be 

 carried cannot be determined. But rapid cell-multiplication, 

 no doubt, brought difficulties ; and in some of the colonies 

 a solution was found of higher character than mere outward 

 expansion. Not only a physical but a psychical change was 

 impending. The individual cells or units of the colony had 

 not as yet shown a disposition to a truly united life. There 

 was no division of labour ; and " each cell for itself " was, so 

 to speak, the motto of the colony. A new modus vivendi of a 

 most startling description was now to be evolved. The 



