Flowerlike Forms and Fantasies i8i 



may offer to the crab, are effective against Its enemies 

 with their stinging weapons of defense. The hermit 

 crab reciprocates by carrying the colony about to places 

 most likely to be plentiful with food; a favor enhanced 

 by the fact that the polyps are also assured of better 

 oxygenation. 



When a colony of Hydractlnia Is examined closely, 

 the Individual polyps will be found to rise from a horny, 

 rootlike network creeping over the surface of the shell. 

 It will further be observed that the zoolds are of three 

 entirely different kinds: a nutritive member carrying a 

 crown of tentacles; a second slender individual without 

 tentacles but well armed with stinging cells, and a 

 shorter stalk on which a small cluster of ovoid bodies 

 Is attached near the top. These latter are the gono- 

 phores. Hydractlnia has no jellyfish stage; the eggs 

 develop Into swimming larvae which seek the shell of 

 some other hermit crab than that on which they were 

 born, and there commence another colony. 



The characteristic feature that distinguishes tubu- 

 larlans from other hydrolds is In their long slender 

 zoold-bearing stems. These In some instances reach a 

 length of ten or more Inches; often they are branched. 

 The zooids ordinarily have two rings of tentacles en- 

 circling the mouth. In many species, however, the 

 mouth Is raised on a prominence, or proboscis; and not 

 infrequently reproductive zooids will be attached be- 

 tween the two rows of tentacles or just below the outer 

 fringe. In no tubularlan does a horny hydrotheca 

 cover the hydranth. 



Such free-swimming colonies of hydrolds as this pool 

 affords are few If not relatively rare. This Is not to 



