PRE-PAL^OZOIC AGES 
Until as tiny sac appears their sphere, 
Close bound by cells disposed in single layer. 
Changes, within and out, slow come to pass 
As cells, begetting cells, swell out the mass. 185 
And by persistent pressure overborne, 
Now is the sphere, at one part, inward drawn : 
And with its cells thus brought to double layers, 
The tiny mass a crescent aspect wears. 
Then draw the crescent horns together near, 190 
And by degrees enclose the indrawn layer ; 
And little ducts are slowly formed between 
The outer cells and those that lie within. 
Of social cells wide changed is now the state 
From that of cells, still living isolate. 195 
No longer does each cell through all its mass 
Alike eat, drink, and waste material pass. 
United, corporate life is now the goal ; 
And labour is divided through the whole. 
Each gives up something, and with greater zeal 200 
Promotes, in special ways, the common weal. 
The outer layer takes up the work without, 
Protects the mass, throws cells as feelers out, 
And seizes food ; whilst in the inner one 
The work of dealing with the food is done. 205 
And slow about the life-mass are devised 
Organs to separate functions specialised. 
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