70 The Study of Animal Life PART i 



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. 



Many are nutritive in form like the little 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 embryos which 

 start new colonies. Then there 

 are long, lank, sensitive mem- 

 bers, also mouthless, which 

 serve 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 

 FIG. 14. -Colony of Hydractinia class of individuals starved, 

 echinata. a, nutritive individuals ; abortive members like the 



0, reproductive individuals ; c, 



abortive spines ; and there are thorns On the hawthorn hedge. 



s^c^dinTeSv^lFrol 5 In recognising their utility to 



Chambers's Encyciop. ; after All- 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 very clearly 

 one law of progress among those animals which form colonies. 

 The crude form of a colony is an aggregate 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- 



