298 CHAPTERS ON EVOLUTION. 



and division of the germ. Conversely, as we ascend the scale of 

 being, we witness as marked a tendency towards concentration and 

 amalgamation of at least the superficial aspects of the organism. 

 The higher animal or plant is not so markedly colonial as the lower 

 organism. Externally, indeed, there may be no trace in the higher 

 organism of compound nature ; whilst, as we have seen, the intimate 

 constitution of its tissues fully reflects its colonial constitution. Then, 

 also, arrest of the process of development seems to increase the 

 tendency towards the colonial organisation. The tapeworms (Fig. 191) 

 may, on good authority, be regarded as animals whose development 

 has been arrested at an early stage of that process. We may readily 

 enough conceive that, but for such arrest, these animals might have 

 progressed towards that higher type of worm structure seen in leech, 

 nai's, or earthworm in which the separate joints practically repre- 

 sent the elements of a colony in close and inseparable union. Thus a 

 leech or earthworm, like the higher animal, is " colonial." It represents 

 the transition stage between a low colony with loosely aggregated 

 units, such as the sponge typifies, and the higher colony in which the 

 units have become closely merged together, as in the bird or 

 quadruped. This view of the intermediate place of these animals 

 is not merely supported by their position in the animal tree, but 

 likewise by the fact that each apparently closely connected joint of 

 a true worm accurately represents the structure and functions of 

 every other joint of the body save, indeed, the specially modified 

 segments of head and tail. The worms and their allies thus become 

 interesting in our eyes, from the fact that they present us with 

 examples of that degree of development which, whilst leading 

 towards union of the original units of the organism, yet leaves their 

 identity sufficiently distinct to permit their ideal separation and the 

 realisation of their originally colonial nature, through the exercise of 

 a free philosophy. 



Thus we again conclude that the primitive and earliest condition 

 of structure in the living series is the " colonial " and compound con- 

 dition. We arrive at this conclusion from a survey of the teachings 

 of development, which shows us, firstly, that everywhere the germ 

 in its earliest state tends to division and multiplication. Secondly, we 

 note that many organisms, such as the lower colonies of protoplasmic 

 forms, or even the mere primitive sponges themselves, remain per- 

 manently in a colonial condition, which would naturally enough 

 represent permanent arrest of development in the early stages of 

 egg-development. Thirdly, we learn that arrest of development, 

 even at a later stage, may produce the colonial organisations of higher 

 types. This latter view meets the case of the tapeworms and of 

 the true worms likewise. In the latter, as represented by the Nai's 

 (Fig. 192), we see the hereditary tendency towards colony-making 



