152 
THE OCEAN WORLD. 
in organic continuity with the polype, which has retired thither more 
or less completely as into a cell. 
Milne Edwards remarks that the polypiers of the Madrepora pre- 
sent in their structure five principal modifications, due in part to the 
fundamental number of which the chambered cells are the multiple, 
and in part to the mode of division in the visceral chamber, and finally 
to the manner in which its tissue is constituted. M. Edwards avails 
himself of this peculiarity of structui’e in order to divide the Madrepores 
into fixed sections ; namely, Madrepore s apores, Madrepores per fores, 
Madrepores tabules, Madrepores tulerlewv, and Madrepores rurjueux. 
in the group of Aporous Madrepores, the polypier is perhaps the most 
highly organized. We find there a well-developed and very perfect 
wall, and a well-developed visceral apparatus. The calyx is neatly 
starred ; the number of rays in the earlier stages being six, which soon 
afterwards reach from twelve to twenty-four. The cells between the 
chambers are sometimes open in all their depth, sometimes more or less 
shut up by transverse plates ; these, being independent of each other, are 
never reunited in the breadth of the visceral cavity, so that they con- 
stitute discoid plates such as we find in tabular and rugose Madrepores. 
The animals belonging to this group, which may be characterised as 
stelliform or star-like, are very abundant in every sea, and in several 
geological formations. They constitute many families, among which 
may be noted the Millepoeina of Ehrenberg, the polypier of which 
Dr. Johnston describes as “calcareous, fixed, plant-like, branching or 
lobed, with cells scattered over the whole surface, distinct, sunk in 
little fosses, obscurely stellate, the lamella? narrow and almost obsolete.” 
(Johnston’s Zoophyte s, vol. i. p. 194.) In Turlmwlia, the animal is 
simple, conical, striped, furrowed externally with larger and smaller 
ribs, the mouth surrounded by numerous tentacula, and solidified by a 
calcareous polypier, which is free, conical, and also furrowed externally ; 
attenuated at the base, but enlarged at the summit, and terminating in 
a shallow radiated lamellar cup or cell. Several species have been dred°ged 
off the coast of Cornwall, and tho west coast of Scotland and Ireland. 
T. meUetiana is described as coral-white, wedge-shaped, somewhat 
compressed, with interspaces or ribs equidistant, smooth, and glossy. 
Above, the ribs turn over the edge, and are continued into the centre 
of the enlarged cup, forming its lamellae. “ That the zoophyte must 
have lived for some time after having become a movable thing, is 
