35 



The polyps are arranged on elongated, diverging stalks in groups of four to 

 five, young polyps arising often in the angle between two older polyp-stalks. 

 They also occur singly on the edges of the lower branches They are small. 



Fig. 20. D. costato- 

 rubra. 



Fig. 20a. D. costato- 

 rubra. — b, from stem 

 cortex ; c, from stem 

 canal walls. 



the length averaging 0-48 mm. and the breadth 0-6 mm. They are placed on the 

 stalk at an obtuse angle, which often approaches very nearly to a right angle. 

 They are roundish oval in shape, the long axis being parallel to the stalk. 

 The younger polyps are much smaller on an average, measuring 27 mm. in 

 length and 03 mm. in breadth. The spicules are arranged in eight double 

 rows, in each of which there are four to five pairs of converging spicules. It 

 is the exception for any of these to project beyond the polyp-head, but in one 

 or two cases the uppermost project a very little. The spicules of the lateral 

 rows are occasionally a little larger, but seldom project at all. The polyp- 

 spicules are somewhat flattened spindles, straight or slightly curved, with simple 

 spines ; they often measure about 0'36 mm. in length, but are usually smaller. 



The Stutzbundel is well developed, consisting of two to three large, and 

 a number of smaller spicules. One of the larger projects considerably, and 

 very often a second also projects. In younger polyps the Stiitzbiindel is not 

 so pronounced but still is (juite distinct, while in the youngest polyps its 

 presence can be detected only from the fact that spicules are more numerous 

 on the dorsal side of the short polyp-stalk. 



Cortical spicules : (a) Those of the stem are slender spindles, straight or 

 curved, 06 to i^ mm. long, 003 to 015 mm. thick. They form an irregular 

 mesh-work, the smaller spicules lying in the larger meshes or running from one 

 mesh to another. This arrangement is marked out by the presence of spicules 

 either pink in colour or with a pinkish core. 



(b) Those of the stalk are large spindles straight or curved, clubs, three- 



