SEA-ANEMONES AND CORAL POLYPS. 21 



er portion extends a mass of tentacles of the richest blue, 

 and, from their armament of lasso-cells, of the most dan- 

 gerous character. They are called Zooids, and are of 

 four kinds. Some aid in locomotion, some are reproduc- 

 tive, while others are feeders for the entire colony. The 

 tentacles are dragged from twenty to one hundred feet or 

 more behind. The beautiful filaments form tempting baits 

 when lowered, and in this way the Physalia feeds. The 

 man-o'-war generally has several tenders, little fishes of 

 the family Scombrida, of the exact color of the death- 

 dealing tentacles, that live under and among them, a won- 

 derful case of mimicry.* 



Allied to the Physalia are the Porpita and Velella. 

 The latter also floats upon the surface, a raft bearing a 

 silvery sail, while beneath is the same rich coloring of the 

 Physalia. 



Works on Hydroids for further reference, 



" Acalephs (Jelly-Fisbes) of North America, with Pictures of most 

 of the Species in Catalogue of Museum of Comparative Zoology," by 

 A. Agassiz ; L. Agassiz, " Contributions to the Natural History of the 

 United States," vol. iv ; " Sea-side Studies in Natural History," 

 Agassiz ; " Sertularian Zoophytes of the Coast of England," T. 

 Hincks ; "Popular Science Review," 1878, p. 223; Huxley's "Man- 

 ual of Invertebrates" ; "Challenger Reports." 



Class II. SEA- ANEMONES AND CORAL POLYPS 

 (Actinozoa). 



Order I. Actinaria. These are well represented 

 by the sea-anemone, 'or Actinia (Fig. 20). In appearance 



* The author once swam over the tentacles of a Physalia with an 

 almost fatal result ; the blue marks were plainly visible six or eight 

 months after. These fishes not only mimic the color of the tentacles, 

 but assume vertical positions v so that they seem actually a part of 

 them. I have often lifted the man-o'-war, which can be safely done 

 by the " sail," and the fishes that were previously unnoticed would 

 dart about in the greatest alarm. A more remarkable case of protective 

 mimicry is not known. 



