57 



Fig. 30. D. crystallina. 



The stalk is short, and the long axis of the polyp-bearing portion stands at an 

 angle to the stalk. 



The stalk is short, measuring 1'2 cm. in length, somewhat thick and rigid, 

 and gives off fi'om its base and for a 

 short distance up the side numerous 

 stolons to which are attached frag- 

 ments of shells and grains of sand. 



The polyparium is pear-shaped 

 and slightly flattened in one plane, and 

 consists of a number of branches which 

 rise almost at a right angle to the 

 stem. The stem rises for a short dis- 

 tance entire, and then gives off a large 

 branch on each side in the plane of 



flattening. Slightly farther up it gives off a second large branch on one side 

 also in the plane of flattening. The larger branches rise at an angle which 

 approaches a right angle, and give rise by repeated divisions to the small 

 twigs which bear the polyps. Over the surface of the stem and branches 

 smaller branches arise, which either bear the polyps themselves or give rise by 

 division to the polyp-bearing twigs. Two of the lowest branches are leaf-like, 

 flattened and reflexed, and almost surround the stalk, leaving two open spaces 

 between the edges of their base of attachment, in which small ordinary 

 branches with a rounded stem are found. 



The polyps are arranged in small groups of five to six, two or three of 

 these being grouped together to form larger bundles. On the edge of the 

 flattened, leaf-like branches the polyps occur singly or in small groups. The 

 polyps are low, shallow, cup-shaped, measuring 0'4 mm. in height and 064 

 mm. in breadth. Each polyp sits at a right angle on a stalk which measures 

 on an average 08 mm. in length. The polyi)-spicules are arranged in eight 

 double rows, in each of which there are five pairs of converging spicules. The 

 upper pair in each row projects for a short distance beyond the polyp, and in 

 the space between the double rows there are one or two pairs of short, thick 

 spicules which run parallel to the sides of the adjacent double rows. The 

 spicules are flattened spindles, either curved or straight, with minute spines on 

 their surface. They measure on an average 024 mm. in length and 0032 mm. 

 in breadth ; the projecting spicules, however, may reach a length of 0'4 mm. 

 On the aboral surface of each tentacle there are two rows of small, flat, blunt 

 spicules, arranged in bluntly converging pairs with their apices directed towards 

 the distal end of the tentacles. 



The Stiitzbundel is well developed, and consists of a number of large 

 spicules which form a support for the polyp-stalk. The spicules may reach a 



