ACTINOZOA. 187 



When growth takes place chiefly in a horizontal 

 direction, the so-called lamellar form of corallum 

 results. Here, the secondary corallites are united 

 throughout their whole height, and disposed in a 

 linear series, the entire mass presenting one con- 

 tinuous theca. Sometimes it is possible to count 

 the number of corallites, but often their several 

 calices merge, as it were, into a single groove, 

 traversed, perhaps, by a columella running parallel 

 to its sides, towards which two opposite rows of 

 septa are seen to converge. 



Both the lamellar and ccespitose forms of coral- 

 lum 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 

 Mceandrina, 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. 



Basal gemmation, among sclerodermic Corals, 

 affords very different products, according as the 

 coenosarc remains soft, or deposits a coenenchyma; 

 appears under the form of stolons, or of stouter 

 connecting stems ; or even spreads out in several 

 directions as a continuous horizontal expansion. 

 In this case it is evident that the latest formed 

 parts of the mass are those which are situated 

 nearest to its circumference. 



The corallites may either appear widely sepa- 

 rated from one another, or closely aggregated 

 and, perhaps, confused by reason of the scanty 

 development of an intervening coenenchyma. 



