CCELENTERATA I ACTINOZOA. I ^ ^ 



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continuity of the loculi " (Greene). The septa, too, are often 

 furnished with styliform or spine-like processes growing from 

 their sides, which often meet so as to form " transverse props 

 extending across the loculi like the bars of a grate, and termed 

 ' synapticulae.' " 



The Zoantharia Sclerodermata are divided into the four 

 following groups, founded upon the characters of the co- 

 rallum : 



1. Tabulata. Septa rudimentary, or entirely absent ; tabulae 

 well developed, and dividing the visceral chamber into a series 

 of stories. 



2. Perforata. Septa well developed ; dissepiments rudi- 

 mentary; no tabulae. Corallum composed of porous scleren- 

 chyma. 



3. Aporosa. Septa well developed, lamellar ; no tabulae. 

 Corallum composed of compact, imperforate sclerenchyma. 



4. Tubulosa. Septa indicated by mere striae ; thecae pyri- 

 form, occasionally united by a basal ccenenchyma. 



GEMMATION AND FISSION AMONGST CORALS. As regards 

 the modes in which the composite corals are produced, the 

 following is a summary of Professor Greene's remarks upon this 

 subject. (See Ccelenterata, p. 203 et seq.) The production of 

 the composite Actinozoa is effected either by gemmation or by 

 fission. In the former method three varieties have been dis- 

 tinguished, termed respectively " basal," " parietal," and " cali- 

 cular " gemmation. 



In basal gemmation the mode of increase is by means of 

 a rudimentary ccenosarc, which is put forth by the original 

 polype, and from which the young polype-buds are produced. 

 It " affords very different products according as the coenosarc 

 remains soft, or deposits a coenenchyma ; appears Bunder the 

 form of stolons, or of stouter connecting stems'; or even 

 spreads out in several directions as a continuous horizontal 

 expansion ; " in which last case the youngest polypes are, of 

 course, those nearest to the periphery of the mass. 



The parietal mode of gemmation is the commonest, and 

 it gives rise chiefly to dendroid, or tree-like, corals. In this 

 method the buds are produced from the sides of the original 

 polype, and they often repeat the process indefinitely. 



Calicular gemmation is not known to occur in any recent 

 coral, but it was a common mode of increase amongst extinct 

 forms. In this method " the primitive polype sends up from its 

 oral disc two or more similar buds ; these, in their turn, produce 

 other young polypes, and thus the process is repeated, until an 

 inverted pyramidal mass of considerable size is produced, all 



