83 



cluster, and as all the polyps reach almost the same level, the surface is nearly 

 even. The heads, which present a beautiful contrast in colour to the rest of 

 the colony, are small, varying from 0'48 to 06 mm. in length, and from 0'36 to 

 0-4S nmi. in breadth, and are placed on the stalk at an angle which varies from 

 I'ight to obtuse. The spicules are numerous 

 and are arranged in eight double rows in 

 each of which there are seven to eight pairs 

 of small spicules, none of which project. 

 They are small, flattened spindles with 

 toothed edges, averaging 0-12 mm. in length. 



The Stiitzbtindel shows considerable 

 variation ; in certain polyps it is well de- 

 veloped, and is formed usually of two to 

 three spicules which may reach a length of 

 5"6 mm. and of which one, or two, may 

 project 0o6 to OG mm. beyond the polyp- 

 head ; in others it is not so well developed, 

 and its projecting part may be almost con- 

 cealed by the polyp's lying parallel to it ; 

 while in yet other cases it is so small that 

 it can scarcely be said to be present. In 

 the majority of cases the spicules are slightly 

 shorter than the above measui'emeuts indi- 

 cate. 



Cortical spicules : (a) Those of the 

 stem are long spindles which form an 

 irregular network in the meshes of which smaller spindles and three-rayed 

 forms occur. This arrangement has a striking effect owing to the contrast- 

 ing colours of the spicules, the larger being pale orange-yellow, and the smaller 

 white ; the contrast is accentuated by the sporadic occurrence of single pink 

 spicules among the large orange forms. The arrangement is continued into the 

 twigs, but here the red colour predominates in the large spicules, the yellow being 

 absent or masked by the red. The large spicules are spindles, straight or 

 curved, with numerous blunt, spine- like processes regularly arranged ; these 

 spindles often divide at one end into a number of prongs which may be wide 

 spread, or crossed over and twined with one another. They vary from 07 to 

 5*0 mm. in length, and from 0-048 to 0-3 mm. in breadth. The three-rayed 

 forms are much smaller, having a maximum length of 0-48 mm., and breadth 

 of 0'36 mm., while the smaller spindles vary from 0-25 to 0'6 mm. in length. 



(Jj) The stalk contains spicules similar to those of the stem, but in addition 

 there are clubs, four- and five-rayed forms, tripod shapes with a thick piece at 



Fig. 41. D. gilva. 



