THE EIGHT-RAYED POLYPS 



3491 



B 



The soft covering of this Gorgonia is white. These animals occupy no very im- 

 portant place in the economy of nature; but several gastropods seem to attack 

 the polyps, and brittle stars climb up the branches in search of food. A beautiful 

 form is Isidigorgia, resembling a corkscrew with a long spiral. It sends off at right 

 angles to the principal axis, and at short intervals, delicate branches, so that the 

 whole structure looks like a spiral staircase constructed of fine cord. The illustra- 

 tion on the opposite page shows an allied 

 form {Streptocaulus) of the family Chryso- 

 gorgoniidce , as yet found only in the West- 

 ern Atlantic. The simple or branched 

 colonies are as thin as horsehair, and the 

 delicate axis has a golden sheen, with a 

 beautiful display of colors. 



The genus his, the stock of which is 

 partly horny and partly purely calcareous, 

 forms a transition between the above and 

 the red coral (Corallium rubrum}. In the 

 latter the axis is calcareous, and built of 

 numerous fine layers, the microscopic 

 structure of which is so definite that a con- 



RED CORAL. 



Part of a stock with retracted polyps, two have 

 been opened (magnified) ; B. With polyps more 

 or less extended; a larva (a) seen in the act of 

 emerging through the mouth of the uppermost 

 polyp. 



STRUCTURE OF ORGAN-PIPE CORAL. 



a. Starting points of new individuals. 



(Natural size.) 



noisseur can detect false from 

 real coral. The fresh axis is 

 covered with fine longitudinal 

 furrows, in which run the 

 deepest of the canals connect- 

 ing the polyps with one another. The stocks, as a rule, consist either purely of 

 male or purely of female individuals, although occasionally the two sexes are found 

 on one and the same stock, and even individual polyps which are both male and 

 female sometimes occur. In the illustration, a slightly magnified branch of a stock 

 is represented, with several retracted polyps and two cut open. In the upper ex- 



ORGAN-PIPE CORAL, Tubipora. 

 (Natural size.) 



