186 FOSSIL ACTINOZOA. 



3. Calicular gemmation. This consists in the production of buds from 

 the calicine disc of the parent corallite, which may or may not continue 

 to grow thereafter, whilst the new corallites thus produced generally 

 repeat the process. This mode of growth is exceedingly rare amongst the 

 Zoantharia sclerodermata, and is never typically exhibited ; but it is a 

 characteristic feature in many of the Rugose corals. In many of these 

 (fig. 74), the original polype throws up from its calicine disc one or more 

 new corallites, which kill the parent. These, in turn, produce others 



after a similar fashion, till the entire 

 corallum assumes the form of an in- 

 verted pyramidal mass resting upon the 

 original budding polype. In other Ru- 

 gose corals the calicine disc gives off 

 but a single bud, which may repeat the 

 process indefinitely till the corallum 

 presents the appearance of a succession 

 of inverted cones placed one above the 

 other. 



4. Fission. This process in the 

 coralligenous Actinozoa is usually ef- 

 fected by " oral cleavage," the divisional 

 groove commencing at the oral disc, and 

 . < 4. -Calicular gemmation as deep ening to a greater or less extent, 



seen in Lonsdaleia flonjonnis. Car- r . . 



boniferous. the proximal extremity always remain- 



ing undivided. According to Dana, in 



fission a new mouth is formed in the disc near the old mouth, and a 

 new stomach is formed for the new mouth, round which the new ten- 

 tacles are then developed. This, therefore, is not, strictly speaking, a 

 subdivision into halves ; since one half carries off the old mouth and 

 stomach. 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 as- 

 sume." 



" The coral-structures which result from a repetition of the fissipar- 

 ous 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 ccespitose, 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 illus- 

 tration of this is afforded by the large gijrate 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 re- 



