THE STRUCTUKE OF XENIA HICKSONI. 285 



at its lower eud, gradually widening from below upwards. 

 The total length of the stem is about 30 ram., its breadth at the 

 base 13 mm. by 6-5 mm., its breadth at the top 23 mm. by 6 mm. 

 The non-retractile polyps {A.) are long and slender, and 

 measure on an average about 15 mm. in length (including the 

 tentacles), though a few specimens reach almost 30 mm. in 

 length. The polyps are 1 mm. to 2 mm. broad. The tentacles 

 of the polvps measure 4 mm. to 5 ram. in length, and bear on 

 the inner side two series of rather slender pinnules, each 

 series consisting of three rows of about sixteen to twenty-four 

 pinnules in each row. In one or two of the tentacles examined, 

 the pinnules at the base are so arranged that it is difficult to 

 say whether they are in three or four rows on each side of the 

 middle line. The pinnules in the middle of the tentacle 

 measure about '5 rara. in length, and are about four times as 

 long as they are broad. The middle line of the tentacle is free 

 from pinnules along the greater part of its length. The polyps 

 are 1 mm. to 3 rara. apart, but they are closer together round 

 the edge of the summit of the stem than on the middle portion 

 of the sumrait. Around the edge of the surarait of the stera 

 there are many small polyps in all stages of development,— in 

 fact, all the polyps near the edge of the surarait are small ones, 

 the large ones being situated in the middle portion of the 

 polyp-bearing area. 



The walls of the polyps are thiu, and when the colony is 

 removed from spirit the polyps fall together and form a con- 

 fused mass on the end of the stem. 



Between the bases of the polyps there are many closely 

 apposed small zooids (fig. 37, S.), quite different in appearance 

 frora buds or young polyps. These siphonozooids are frora six 

 to ten times as numerous as the polyps or autozooids, and they 

 occur all over the summit of the stem. The siphonozooids are 

 all similar in appearance, being cylindrical or club-shaped, 

 2 mm. to 5 mm. in length and "5 mm. to 1 mm. in diameter. 

 The tentacles are eight small rounded lobes arranged round 

 the mouth; they are never longer than '25 mm., and never 

 possess pinnules. 



