INTEODUCTION. 



The Polyzoa are almost universally composite animals*, 

 forming colonies, often of considerable extent, which 

 are the product of repeated, continuous gemmation. 

 They are all inhabitants of water, and for the most part 

 of the sea; but a comparatively small though very 

 interesting group has its home in fresh water — in river, 

 stream, pond, or lake. 



They present the greatest variety of form and habit, 

 which cannot be generalized in any definite formula. 

 Sometimes they grow in plant-like tufts, composed of 

 series of cells variously linked together ; sometimes they 

 spread over shell or stone, like the finest lacework 

 or fairy chains ; sometimes they rise into stony corals, 

 or broad and flexile fronds. At times they bury the 

 seaweed beneath their fleshy crusts, or invest it with 

 silvery network. In many of the stony kinds the cells 

 are richly sculptured and exhibit an immense amount of 

 microscopic ornament ; in others the colonies are built 

 up of exquisite little frosted tubes, often gracefully 



* The only known exceptions are tlie members of the genus Lqxosoma, 

 Keferstein. 



