FOUNDATIONAL AGES 13 



symmetry with which quiescent life can confront conditions. 

 Their stings were probably the organs that first raised, in an 

 acute form, the puzzling problem of pain. 



From the primeval colonies which, on separate lines of 

 evolution, had given rise to sponges, and to stinging animals, 

 another line was struck destined to lead to far more important 

 results. This departure was evidenced by creatures which, 

 in those remote times, are best classed under the comprehen- , 

 sive appellation of Worms. As the result more or less of 

 boring into the mud and sands of the shallows, the bodies of 

 these animals became elongated and two-sided. And although 

 most forms, no doubt, were of a plump and stumpy aspect, 

 they presented a very different appearance from the sedentary 

 and rounded stinging animals. As regards, however, internal 

 organisation, some of them were probably not greatly in 

 advance of the latter. In course of time several internal 

 changes were effected. The channel used at one end as a 

 mouth became a complete thoroughfare through the length 

 of the body ; whilst the original stomach-like chamber was 

 rendered more complex by the formation of a second enclosed 

 space (cesium). In this new apartment some of the labours 

 of the old cavity were carried on, and other functions were 

 also undertaken. Division of labour a cardinal feature 

 of progress was therefore carried farther. 



Some of these more advanced worms were probably expert 

 swimmers ; but at one period certain of them adopted 

 sedentary habits. In course of time their descendants became 

 so sedate that the lower part of the body became fixed in 

 the ground. Brought to this condition, they developed 

 outwardly a five -sided and more or less radial symmetry. 

 These animals formed the parent-stock of the spiny-skinned 

 creatures (Echinoderms) ; and a certain amount of free 

 existence was in course of time recovered. Cystids, sea-lilies,, 

 sea-urchins, starfishes, brittle-stars, and sea-cucumbers were 

 the outcome of this line of Evolution. 



Meanwhile other of the worms pursued another evolutionary 

 course. A well-marked head was developed, a thick muscular 

 surface was formed on the under-part of the body, and the 

 scattered nerves underwent a considerable amount of concen- 



