﻿12 EVOLUTION IN THE PAST 



consist of an outer and inner layer of cells (Gastrula stage). 

 Some division of labour was impending and in time became 

 evident. The outer cells gradually took up as their duties 

 matters of protection, reproduction, and arranging lines of 

 communication with the interior. These several labours, 

 however, were not separately discharged by cells of different 

 character ; for the outer cells in great part retained their 

 original versatility. The duty of the inner cells was more or 

 less confined to promoting, by means of little lashes, a flow 

 of the food-bearing water through the whole body of the 

 colony. There was, therefore, a certain amount of labour- 

 division, although of primitive description. As, however, 

 there was no thorough differentiation and co-ordination of 

 the cells, the transformed colony lacked individuality. 

 Even to-day the cells of a sponge are far from being in a state 

 of complete co-ordination. The porous edifice is not the 

 residence of an ego. 



Sponges of various forms and degrees of organisation 

 must have made their appearance before the Cambrian times. 

 Very early in their career they settled down to sedentary 

 lives ; and it is not supposed that they led to the appearance 

 of any life-forms of higher grade. This line of animal evolution 

 — savouring somewhat of the vegetable — was not, therefore, 

 momentous. 



Sprung from the same stock as sponges, and for a time, no 

 doubt, retaining close affinities with them, other organisms 

 slowly appeared. These transformed colonies gradually 

 developed into hydras, jellyfishes, corals, sea-anemones, 

 and allied forms. These animals enjoyed the distinction of 

 possessing a mouth, opening into a cavity in which digestion 

 was carried on. This cavity had also duties to discharge 

 relating to circulation. Nerves — unknown to Sponges — were 

 in a primitive stage of evolution ; and certain cells became 

 transformed for stinging purposes. The various cells were, 

 no doubt, so far co-ordinated as to constitute an individuality. 

 Altruism, therefore, had resulted in a bigger ego. 



The animals never gained the distinction of possessing 

 either heads or hearts. Becoming more or less sedentary in 

 habit, they developed roundness of structure — the best 



