208 



TOILERS IN THE SEA. 



and inner edge ; they possess eight tentacles, and 

 these are ciliated on one side. According to recent re- 

 searches, the polypes of each pen are either all male or 

 all female, so that all the members of one community 

 are of the same sex (fig. 41). The British species is 

 called by the fishermen the 

 " cock's - comb," but this is 

 scarcely so expressive as sea- 

 pen. "It is from two to four 

 inches in length, and of a uni- 

 form purplish-red colour, except 

 at the tip or base of the stalk, 

 where it is pale orange-yellow. 

 The skin is thickish, very tough, 

 and of curious structure, being 

 composed of minute crystalline 

 cylinders, densely arranged in 

 straight lines, and held together 

 by a firm gelatinous matter or 

 membrane. These cylinders 

 (spicules) are about six times their diameter in length, 

 straight and even, or sometimes curved and bulged, 

 and of a red colour, for the colour of the zoophyte is 

 derived from them, and they are accordingly less 

 numerous where the purple is faint or defective. 

 The stalk is hollow in the centre, and contains a long 

 slender bone which is white, smooth, square, and 

 tapered at each extremity to a fine point. It does 



FIG. 40. 

 THE THORNY SEA-PEN. 



