58 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
on secondary branches and the twigs which spring from these. The secondary 
branches are crowded closely on the primary and form catkins 1°5 to 2°5 em. 
in length, the larger catkins being of a compound character. 
In the cortex of the terminal polyp-bearing branches there is a longitudinal 
arrangement of the spindle-shaped spicules, and this is continued on to the 
dorsal surface of each polyp-stalk. 
The polyp-heads are bent sharply on the polyp-stalks, so that the tentacular 
surface faces the cortex of the terminal twigs. 
The cortical spicules of the stem and main branches form by interlacing 
a continuous armature. These spicules are of very diverse and distinctive 
forms, including the following :— 
(a) Boat-shaped spindles with few warts. 
(6) Curved spindles with long spines, which are more developed on the 
convex surface. 
(c) Very spinose club-like forms. 
(d) Triradiate spinose bodies. 
(e) Irregular spinose bodies. 
The following measurements were taken of length and breadth in milli- 
meres -— 
(a) Boat-shaped spindles : 0°8 x 0°15 ; 0°75 x0°075 ; 0°67 x01; 0°62x 
0-1; 0°5 x 0:075; 0°45 x 0:09. 
(6) Curved spindles: 0°95 x 0:15 ; 0°85 x 0°12; 0°8x0:15; 0°73 x 0°15; 
On 0 O1ba 0 lon 0292 x02. 0 eO-e 
(c) Club-like forms: 0°33 x 0°25. 
The spicules of the polyp-head and polyp-stalk include long curved or 
sinuous spindles with knob-like warts which in some cases are more numerous 
and better developed at the tips of the spindles; also spindles with only a 
few poorly developed spines. 
The following measurements were taken of length and breadth in milli- 
metres :— 
(1) Spimose spmdles: 15x01; (l5x0-1; 11x012; 0 oea0tee 
0°4 x 0°05 ; 0°2 x 0°02. 
(2) Smooth spindles with only a few spines: 1:2x0:09; 0:9x0°:05 ; 
0°69 x 0°05. 
The spicules of the canal walls consist of spindles similar to those of the 
cortex, but the form with few spines predominates. 
The following measurements were taken of length and breadth in milli- 
metres :— 
(1) Spinose spindles: 0°87x 0°12; 0°85 x0°12; 0°83x0°12; 06x01; 
0°55x 013; 0°5 x Ol. 
