THE HYDRA. 33 



cialization, so evident in the development of animals, has 

 its parallel in the development of civilization or in the 

 development of a trade. For example, the early cobbler 

 tanned his own leather, whittled his own pegs, made his 

 own thread, lasts, etc., and then made the shoe. But, as 

 the trade of shoemaking developed, one man began giving 

 his whole time to making the leather ; another, to making 

 the lasts, etc. ; and another, to making the shoe. To see 

 how much further than this the division of labor in shoe- 

 making has gone in our own time, we need only to visit a 

 modern shoe factory. 



When the cobbler gave up to the tanner the making of 

 the leather, he became a more skillful shoemaker, but lost 

 his skill at tanning. So, when the thread cell of the 

 hydra becomes differentiated for capturing food, it excels 

 in that one thing, but it loses its capacity for doing other 

 things. Here we come upon the universal principle, that 

 precise adaptation to any one thing involves limitations in 

 other things. 



Division of labor develops greater skill and better 

 products in a trade, higher powers and capacities in 

 animal life. While there are many things which cells 

 and cobblers may leave to be done by others, to the ad- 

 vantage of all concerned, there are yet other things which 

 each must continue to do individually. For example, the 

 thread cell, though it may be relieved of the work of 

 digesting its food, must continue to absorb the digested 

 food as it is furnished, and assimilate it; must absorb 

 oxygen, and must excrete waste oxidized materials for 

 itself, so long as it continues a living cell. 



The hydra and the sponge are representations of the 

 Coelenterata, a large and important group of animals, 

 almost exclusively marine. 



NEED. ZOOL. 3 



