ALCYONOID POLYPS. 93 
the large and well-developed polyps, there were multitudes 
of small wart-like prominences, each of which proved to be 
a polyp, but very small and imperfectly developed, having 
only two lamelle in the interior instead of the usual eight, 
and without distinct tentacles, or the ordinary nettling cords 
within. 
Among the other forms of Zoéphytes in the Pennatula tribe 
are those having a stout axis. with branches either side, 
arranged regularly in plume-like style (the Pennatulide); 
or a very slender stem and very short lateral polyp-bearing 
pinnules or processes along it (the Virgularide); or a thin 
reniform shape (Renillidz). Others differ from the preceding 
in having the polyps not retractile; and some of these have 
a slender stem and the polyps arranged along one side of it 
(the Pavonaridz) ; and still others a terminal cluster of polyps 
(the Umbellularide). 
The most of the species secrete a slender, horny axis, and 
have slender calcareous spicules among the tissues, somewhat 
like those of the Gorgonidz. By the thickened base of the 
stem these species anchor the corallum in the mud. Many 
species occur in the deep seas, some at depths of two thou- 
sand fathoms. Moreover, they are brilliantly phosphores- 
cent; and Moseley says that the depths may be in places 
lighted by patches of these species and “ possibly the animals 
with eyes congregate around these sources of light.” 
The Heliopore are peculiar among the Alcyonoids in havy- 
ing a solid compound corallum, of rather large size; and 
they are alone among corals in having a blue color within. 
The corallum consists of slender tubes with intervening cel- 
lular coenenchyma; and as the tubes are crossed by tabula, 
though distantly, Heliopora has been referred to the Tabu- 
late, and also to the Milleporids. It was shown to belong 
