112 



Fig. 55. D. rubeola. 



The exact shape of the polypariuni is difficult to determine owing to a 

 branch or two being absent, but it is most probable that it was of a somewhat 

 oval shape, the long axis standing at right angles to the stalk. In arrangement 

 it is very open — cylindrical branches give ofi' smaller branches which by a 

 repeated dichotomy give rise to the polyp-bearing twigs. The lower branches, 



two in number, are flattened, leaf-like 

 structures which surround the stem and 

 are reflexed, thus forming a collar for the 

 upper portion of the stalk. From the 

 upper surface of these flattened branches 

 two lai'ge cylindrical branches are given 

 off: 



The polyps are arranged in small 

 groups of four to eleven, these groups 

 not being massed into larger ones, but 

 standing apart from one another at the 

 ends of the branches, all the members of 

 a group reaching practically the same 

 level. They are low and round, 0'48 

 mm. high, 064 mm. broad, and are 

 placed at an obtuse, often at a nearly right, angle on the short stalk (about 

 0"5 mm.). The spicules are small and very numerous and are arranged in eight 

 double rows each containing numerous (at least nine) pairs of converging 

 spicules. They form a complete casing for the polyp and average U'17 mm. 

 in length, and 0-032 mm. in breadth. On the aboral surface of the tentacles 

 there are two rows of flat spindles whose ends alternate with one another. 



The Stiitzbundel is well developed, although it is only in a few polyps of 

 each group that it attains its maximum growth. It consists of a number of 

 spicules which form a sheath for the stalk and average 11 mm. in length, 

 scarcely, if at all, projecting beyond the polyp. In a few cases the spicules 

 are 27 mm. long and project for a distance of 08 mm. 



Cortical spicules : (a) In the stem there are slender spindles, straight or 

 curved, with small simple spines, from 0'24 to 2'2 mm. long, from 0'032 to 

 014: mm. broad, colourless to faint brick-red in colour, and in a few cases 

 bifid at one end. 



(/>) In the stalk there are spindles, clubs and numerous irregular forms, 

 either fusiform, globular or radiate. All are covered by numerous, large, simple 

 or branched spines. Spindles are from 0-24 to r2 mm. long and from O'OS to 

 016 mm. broad. The spines are often largely developed along one side through- 

 out its length. 



Canal-wall spicules : (a) In the stem the spicules are spindles with few 



