59 



of the priiK'iiial branches, smaller cylindi-ical Itranches are given off which by 

 division give rise to the polyp-liearing twigs. Two of the lower branches are 

 flattened, leaf-like structures, one of which, much larger than the other, almost 

 surrounds the stem with its broad base, while the 

 other with its smaller base fills up the remaining 

 space, leaving only two small free spaces between its 

 edges and the edges of the other. They are reflexed 

 and form a collar to the upper part of the stalk. 



The polyps are arranged in small groups of four 

 to eight on widely divergent stalks, and singly or in 

 small groups on the edges of the flattened branches. 

 They are low and oval in shape, and are placed at a 

 right angle on the stalks (2 mm. long), and average 

 0-5o mm. in height and 0-(5(} mm. in breadth. The 

 polyp-spicules are arranged in the following manner : 

 The lower polyp-spicules are either arranged horizon- 

 tally, or there are three pairs of spicules which meet 

 at an obtuse angle ; then a ring of horizontally placed 

 spicules three deep ; surmounting this are eight points, 

 each consisting of two or three converging spicules 

 which project beyond the polyp. (3f these converg- 

 ing spicules one is much larger than the other, or 

 others, for it is often opposed by two. In the space 

 between the adjacent points there lie two smaller 

 spicules of about 015 mm. in length which are parallel 



to the converging spicules, one lying usually close beside the larger projectnig 

 spicule. The lower polyp-spicules average 0'33 mm. in length, the upper con- 

 verging spicules measure about 0'45 mm. and project from 0*24 to 0'3 mm. 

 beyond the polyp. On the aboral surface of each tentacle there are two rows 

 of small rod-like spicules. 



The Stiitzbiindel is well developed, and has one oi" two .spicules projecting 

 beyond the polyp, and sometimes the tip of a third may also be seen. These 

 spicules measure aliout 2'8 mm. in length and project for a distance of (J"84 mm. 

 Often the Stiitzbiindel is not so well developed, but this is undoubtedly a 

 younger stage. The arrangement of the spicules on the polyp-stalks is worthy 

 of notice. Along the ventral side there is a dividing line, and from this the 

 spicules are regularly arranged obliquely and transversely, sloping towards the 

 tip on each side. 



Cortical spicules : (a) In the stem there are long spindles with numerous 

 regularly arranged rough warts. They are either straight or curved, often 

 with a bifurcation at one end, and vary from 0'42 to 3'0 mm. in length and 



Fig. 31. D. andamanensis. 



