PRE-DETERMINATION IN NATURE 333 



The argument, as we have seen in a previous chapter, for the 

 animal nature of Eozoon depends on our assuming certain 

 parts of this fixity. We suppose that then as now calcium 

 carbonate had been selected as the material for the skeletons 

 of such creatures ; that then, as now, minute tubuli and large 

 canals were necessary to enable the soft animal matter to per- 

 meate and pass through the skeleton, and that the protoplas- 

 mic animal matter of these far back geological periods had the 

 same vital properties of contraction and extension, digestion, etc., 

 that it has to-day. Could any one prove that these determina- 

 tions of vital and other forces had not been established, or that 

 living protoplasmic matter, with all its wonderful properties, 

 had not been constructed in the Laurentian period, the exist- 

 ence of this ancient animal would be impossible. Yet how 

 much is implied in all this, and though nothing is more un- 

 stable chemically or vitally than protoplasm, if it were intro- 

 duced in the Laurentian, it has continued practically unchanged 

 up to the present time. 



If we pass on to the undoubted and varied life of the 

 Cambrian period, we shall find that multitudes of things which 

 might have been otherwise were already settled in a way that 

 has required no change. 



In the oldest Trilobites the whole of the mechanical con- 

 ditions of an external articulated skeleton had been finally 

 settled. The material chitinous or partly calcareous, its micro- 

 scopic structure, fitted to combine lightness and strength with 

 facility for rapid growth, the subdivision of its several rings, so 

 as to form a protective armour and a mobile skeleton, the 

 arrangement of its spines for defence without interfering with 

 locomotion, the contrivance of hinge joints arranged in different 

 planes in the limbs, — all these were already in full perfection, 

 and just as they are found to-day in the skeleton of a king- 

 crab or any other Crustacean. They have, it is true, been 

 modified into a vast number of subordinate forms and uses, 



