THE AXLAIAL LIFE OF THE GROUP. 481 



sembling' sea-mnsses that it is with ditficulty that the untrained observer is 

 convinced that they ;ii-e really animal eiilonies. Some of the nenera "■' are 

 ■\vell-kuown animals and occasionally tigured in general reference books. The 

 Hawaiian sjjecies in every ease are rarer forms that can only be recognized by 

 experts when aided by elaborate descriptions. 



In this connection mention should be made of certain colonial hydroids ■*o 

 that secret masses of carbonate of lime out of which the animal protrudes like 

 a coral polyp. They are usually pink or orange-colored, and are often called 

 corals. Several species are found veiy plentifully on our coral reefs. On 

 close examination it will be seen that the\' differ in structixre from the true 

 corals. The solid-looking masses with lobed processes, or bosses, are the most 

 CI nimon,-" though tine branching exami)les ^- also occur. In both families the 

 whole surface can he seen, with the aid of a lens, to be covered with small 

 pore-like openings. If a vertical section is examined, indistinct layers can be 

 seen running parallel with the outer surface. Only the surface is alive, the 

 inner mass being composed of the dead skeletons. Thus these animals secrete 

 lime and build up a coral-like sk-elctoii in iiiuch the same way as do the true 

 corals, which are poh'p colonies and (.(iiite different in their organization, 

 though secreting similar masses of lime. 



Zoologists often cite this peculiar fact as an example of "convergence," 

 meaning thereb.y that two animals of ditl'erent types have become adapted to 

 similar conditions of life and come to superficially resemble each other. Other 

 animals, as whales and fishes, birds and bats, show similar evidence of con- 

 vergence. Indeed:, it has not been uncommon for naturalists to j)lace totall.v 

 different animals in the same groirp on account of their resemblance. The 

 Hawaiian HydrocoralUnxe have not been fully studied as yet, and there appears 

 to be no list of even the common species. 



The Portuguese I\I.\n-of-W.\u. 



Sea-bathers occasionally make the acquaintance of the Portuguese man- 

 of-war,*3 ^\'hieh is perhaps the best known member of a third family ** of the 

 .jellyfish trilie. It floats, by means of an air sack, on the surface of the sea. 

 Its stinging jiower is tremendoiis, producing a maddening, scalding pain which 

 lasts till- hours. As the stinging tentacles are long and thread-like and float 

 out loosely in the water, the beautiful "blue bottles" are things that can be 

 more safely admii-ed at a considerable distance. On the windward shore of all 

 the islands they are often stranded by thousands by the ebbing tide, where they 

 dry down to a mere bubble in a few hours. 



Sea Money. 



Anotlier common form ^'' is a flat coin-sliaped disk with fine radiating 

 white lines. About the edge are innumerable fine tentacles. The animal, 



»» AVrfwdirio, Campamilnrla and Plumularia. *" BydrocornUimr. " MiUeporidce. 



*- Stylastf.rida;, *=* Physalia utriculua. ^* Siphonophorce. *^ Porpita pacifica. 



