﻿14 EVOLUTION IN THE PAST 



tration. These animals, it is supposed, gave rise to primitive 

 molluscs ; and in course of time sea-snails, mussels, nautiluses, 

 and allied forms made their appearance. These, however, 

 were the only fruits on this branch of evolution. 



Certain of the worms, however, developed more in accord- 

 ance with primitive promise. The nerves became concentrated 

 in the head region ; a brain was gradually formed, and real 

 intelligence dawned in animal life. In some forms — long 

 sensitive to light only — eyes were slowly evolved. And 

 these animals were probably the first inhabitants of earth to 

 see anything of their surroundings. 



In course of time some of the worms, in correspondence 

 with internal modifications, became ringed or segmented 

 (Annelids) ; and lateral outgrowths were developed for 

 plodding about the shallows. In ringed worms of marine 

 habits, worm-life reached its highest level of development. 

 The head, it would seem, is a more ancient institution than the 

 heart, for worms never developed what can be called " a seat " 

 for their affections. 



Ringed worms played a great part in Evolution, for it 

 was from their ranks that important divergences took place. 

 One line of evolution led to brachiopods or lampshells, and 

 polyzoans ; another to an arthropod stock, which in course of 

 time branched out into a variety of forms (trilobites, king- 

 crabs, shrimps, scorpions, etc.). The pioneers of the several 

 departures were, no doubt, very small animals of their kind. 



How far life advanced in the course of the Foundational 

 Ages cannot be definitely ascertained. But from scanty pre- 

 Cambrian remains, and from the known life of the Cambrian, 

 it may be inferred that invertebrates were represented in all 

 main departments before that Period commenced. Fishes 

 must certainly have had remote ancestors in pre-Cambrian 

 seas, but the ancestral forms are quite unknown. For a long 

 time they probably bore close resemblance to the unsegmented 

 worms well on the road to the evolution of the spiny-skinned 

 animals (Echinoderms). 



In the absence of reliable evidence until much later times 

 it is difficult to speak of the progress of vegetation in the 

 Foundational Ages. But on its humbler plane it no doubt 



