FOSSIL ACTINOZOA. 95 



the proximal extremity always remaining undivided. More 

 rarely, fission " is effected by the separation of small portions 

 from the attached base of the primitive organism, whose form 

 and structure they subsequently, by gradual development, tend 

 to assume." 



" The coral structures which result from a repetition of the 

 fissiparous process are of two principal kinds, according as 

 they tend most to increase in a vertical or in a horizontal 

 direction. In the first of these cases the corallum is cczspitose, 

 or tufted, convex on its distal aspect, and resolvable into a 

 succession of short diverging pairs of branches, each resulting 

 from the division of a single corallite." In the second case 

 the coral becomes lamellar. " Here the secondary corallites 

 are united throughout their whole height, and disposed in a 

 linear series, the entire mass presenting one continuous theca." 

 Both these forms of corallum " are liable to become massive by 

 the union of several rows or tufts of corallites throughout the 

 whole or a portion of their height. An illustration of this is 

 afforded by the large gyrate corallum of Meandrina, over the 

 surface of whose spheroidal mass the calicine region of the 

 combined corallites winds in so complex a manner as at once 

 to suggest that resemblance to the convolutions of the brain 

 which its popular name of Brain-stone Coral has been devised 

 to indicate." (Greene, ' Manual of Ccelenterata,' p. 185 et seq.) 



Fig. 48. Phillipsastrcea Vemeuilli'. From the Devonian (Corniferous Limestone) 



of N. America. 



DEEP-SEA CORALS AND REEF-BUILDERS. At the present 

 day, as has been specially insisted on by Dr Martin Duncan, 

 we find two great groups of the Sclerodermic Zoantharia viz., 

 those which inhabit tolerably deep water, and those which 

 build the great masses of coral which are known as " coral- 

 reefs." The deep-sea corals, though often attaining, as in- 

 dividuals, a considerable size, and though often compound, 



