66 THE ANTHOZOA 



There are both solitary and colonial Scleractiniae, and both 

 solitary and colonial forms occur in the two groups Aporosa and 

 Perforata. The colonial forms are produced by asexual reproduc- 

 tion either by gemmation or division, the resulting individuals 

 remaining in connection with one another. Several of the solitary 

 Scleractiniae reproduce themselves asexually by discontinuous 

 budding or division. Blastotrochus nntrix, a member of the family 

 Flabellidae, produces lateral buds on the theca, which after a 

 time drop off, and a new bud may be formed from the scar 

 of the old one. Some species of Flabellum reproduce them- 

 selves asexually by transverse fission. lUiodopsammia }mrallela 

 and It. socialis, perforate corals, bear marginal and lateral buds 

 which may detach themselves. In the genus Fungia, the discoid 

 free adult forms are asexually produced from an attached parent 

 stock termed the trophozooid, and the adult individuals may 

 multiply themselves by transverse fission. 



In the formation of colonies by asexual reproduction, the 

 distinction between gemmation and division must be borne in 

 mind. In the former case the young zooid, with its corallum, 

 arises wholly outside of the cavity of the calyx of the parent 

 zooid, and the component parts of the young corallum, theca, 

 septa, columella, etc., are formed anew in every individual pro- 

 duced. In division a constriction divides a zooid into two or 

 more equal or iinequal parts, and the component parts of the two 

 (or more) coralla so produced are severally derived from the 

 corresponding parts of the dividing corallum. 



Gemmation in the colonial Aporosa and Perforata always 

 proceeds from the soft tissues which clothe the outside of the 

 theca, i.e. from the edge-zone or its derivatives. In the case of an 

 aporose coral a bud is formed on the edge-zone, and develops into a 

 new zooid with its corallum. The cavity of the latter does not 

 communicate directly with the cavity of the i)areiit, but organic 

 connection between parent and offspring is effected by means of 

 the edge-zone. As growth proceeds, and parent and bud become 

 separated further from one another, the sheet of soft tissues 

 connecting the two loses the characters shown in Fig. XXXI. 

 1, A, the peripheral continuations of the mesenteries are no 

 longer present, and there is found instead a sheet of tissue resting 

 upon projecting spines of the corallum, ])etween which run canals 

 lined by endoderm, the last-named serving as the means of com- 

 munication between zooid and zooid (see Fig. XXXI. 1, B). 

 Such a sheet of soft tissue, devoid of the ])eripheral continuations 

 of the mesenteries, and bridging over the spaces l)etween the 

 zooids, may be called the coetwsarc. Tlie layer of oalicoblasts 

 on the lower surface of the coenosarc gives rise to a secondary 

 deposit of carbonate of lime, which more or less fills up the spaces 



