70 



The Study of Animal Life 



PART 1 



result from the fact that in such a large colony perfect 

 uniformity of nutritive and other conditions is impossible. 

 Individuals which are fundamentally and originally like one 

 another grow to be different, and perform different func- 

 tions according to the caste to which they belong. 



I\Iany are nutritive in form like the httle freshwater 

 Hydra — tubular animals with an extensile body and with a 

 terminal mouth wreathed round by mobile tentacles. On 



these the whole nutrition of the 

 colony depends. Beside these 

 there are reproductive " per- 

 sons," which cannot feed, 

 being mouthless, but secure 

 the continuance of the species 

 and give rise to embn,-os which 

 start new colonies. Then there 

 are long, lank, sensitive mem- 

 bers, also mouthless, which 

 ser\^e as the sense-organs of the 

 colony, and are of use in de- 

 tecting food or danger. When 

 danger threatens, the polypes 

 cower down, and there are left 

 projecting small hard spines, 

 which some regard as a fourth 

 class of individuals^ — staned, 

 members like the 



Fig. 14. — Colony of Hydracthiia. 



echinata. a, nutritive individuals ; abortive 



b, reproductive individuals ; c, 



abortive spines ; and there are thoms On the hawthom hedge, 



also long mouthless individuals 

 specialised in sensitiveness. (From 

 Chambers's Encyclop. ; after All- 

 man). 



In recognising their utility to 

 the colony as a whole we can 

 hardly overlook the fact that 

 their life as individuals is practically nil. They well illus- 

 trate the. dark side of division of labour. 



Herbert Spencer and Ernst Haeckel have explained veiy clearly 

 one law of progress among those animals which form colonies. 

 The crude form of a colony is an agg7-cgate of similar individuals, 

 the perfected colony is an integrate in which by division of labour 

 greater harmony of life has resulted, and in which the whole colony 

 is more thoroughly compacted into a unity. Among the Stinging- 



