THE EARTH FOR MANKIND 539 



division of labor and good teamwork. Those who think of the 

 struggle for life in a simple, shortsighted way sometimes im- 

 agine that the greatest gain to individuals, and therefore to the 

 race, comes when each one tries to get the best of his neighbors ; 

 but the experience of the race and everyday observation con- 

 vince us that the great gains have been made through coopera- 

 tion and joint action. The principle of community action is 



Fig. 222. Colony of Hydractinia 



In this colonial animal (related to the jellyfish and to corals), as in many others, 

 there are distinct kinds of individuals, called hydranths. a, vegetative, or food- 

 getting, hj'dranths, which take in and digest food for the whole colony; b, vegetative 

 hydranths in various stages of contraction; c, protective, or fighting, hydranths, which 

 bear large numbers of nettling cells; d, reproductive hydranths, male and female, 

 which throw off sperm cells and egg cells respectively; e, buds, or undeveloped hy- 

 dranths. (Photograph from model in American ^luseum of Natural History) 



illustrated at every level of life, and is in fact the basis for all 

 higher organisms ; for we may well consider that a many-celled 

 organism is one in which the lumps of protoplasm, instead of 

 separating as fast as they are formed, remain in contact and 

 gradually divide up the special functions among themselves. 

 The division of labor is slight among the simplest many-celled 

 organisms (the hydra and some algae) and increases as we go 



