THE STRUCTURE OF XENIA HICKSONI. 183 



10 mm. to 30 mm., and in breadth from about 4 mm. to 10 mm. The 

 total height of the colony from the point of attachment to the tips of 

 the highest polyps is 50 mm. 



The polyps are, for the greater part of their length, bound together 

 in bundles of about forty to sixty, each bundle forming one stem of the 

 colony. The free portions of the polyps arise from the slightly 

 expanded umbrella-shaped area at the distal end of each stem. Many 

 of the polyps stand almost perpendicularly to the convex disc, but 

 those near the edge of the disc hang downwards towards the base of 

 the colony. The polyps are closer together near the edge of the 

 umbrella, being here "5 mm. to - 7 mm. apart, whereas in the middle of 

 the umbrella they are 1 mm. to 2 mm. apart. 



Polyps (PL XIX., Fig. 2). — The polyps, or, more correctly, the free 

 portions of the polyps, are non-retractile and moderately long and 

 slender. The tentacles are half to two-thirds as long as the body of 

 the polyp. Each tentacle bears on its inner side numerous short, 

 conical elevations with rounded ends. These correspond to the 

 pinnules found on the tentacles of other Alcyonaria. 



The colour of the colony in spirit is light brown. 



As mentioned above, the free portions of about forty to sixty fully 

 developed polyps project from the umbrella-shaped area at the distal 

 end of each stem, but besides these there are several younger polyps or 

 buds in various stages of development, and these are invariably 

 situated on the edge of the umbrella. 



In fully developed specimens the following are the measurements : — ■ 

 " Body " of the free portion of the polyp 4 mm. to 7 mm. long, and 

 TO mm. to T2 mm. broad. Tentacles 2 mm. to 5 - 7 mm. long, and 

 •75 mm. broad. The total length of the adult polyps is thus 6 mm. 

 to 12 mm. 



The body of the polyp is cylindrical and its wall moderately strong. 

 In several of the Xeniklce the body-wall of the polyp is so weak that 

 when the colony is taken out of spirit the polyps fall together into a 

 mass. In this species, however, the body- wall is just strong enough to 

 support the polyps in an upright position, so that on removing the 

 colony from spirit the polyps do not hang limply, but remain standing 

 approximately in their natural positions. 



Tentacles and Pinnules (PI. XIX., Figs. 2 and 3). — Each polyp bears 

 eight tentacles, each of which is provided with numerous pinnules. 



