192 



ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1917. 



is by a bud aj)peai'ing on the surface of the soft tissues outside the 

 circle of tentacles (pi. 2, fig. 1) ; the other method, known as fission, 

 is by a mother coral polyp dividing eqvially or unequally and form- 

 ing two or more polyps (pi. 2, fig. 2). Budding or fission may be 

 repeated until from an initial polyp only 1 or 2, or perhaps 5 milli- 

 meters in diameter, a colony, a compound coral, many feet in diam- 

 eter may result, with thousands of individual polyps, each having its 

 own more or less clearly recognizable mouth, but all joined together 

 by communal soft tissue known as coenosarc. 



Corals that remain simple may be small, 5 or 6 millimeters (about 

 one-fifth inch) in diameter, or they may be rather large, up to as 

 much as 250 millimeters, nearly a foot, in diameter, as in some species 



of the genus Fungia (pi. 3, 

 figs. 1, la). The range in size 

 of the individual polyps in 

 compound corals is from less 

 than 1 millimeter (0.039 inch) 

 in diameter up to as much as 

 2 or 3 centimeters (0.78 or 

 1.18 inch), and perhaps 

 more. 



Coral colonies are very di- 

 verse in form — they may be 

 low, flat plates, closely adher- 

 ent to the basal support ; they 

 may be c ushion- shaped, • 

 they may form more or less 

 perfect hemispheres or 

 spheres; or the outer surface 

 may be variously lobed. 

 Some corals form simple or 

 divided columns ; others form 

 elongate, round branches, 

 which range from only a few millimeters to several centimeters 

 in diameter; the branches of other corals are more or less com- 

 pressed and platelike. Other growth-forms are erect or subhori- 

 zontal, thick or thin plates and vases, which may be small and shal- 

 low or large and deep. Some colonies are tuftlike. In colonies that 

 are formed by budding, the individual corallites and polyps are 

 usually subcircular in outline and are separated from one another 

 by interspaces that range in width from mere dividing walls up to 

 several centimeters across. But in colonies formed by fission, the 

 corallites often occur in series which may contain two or three, or 

 very many corallites in rows; when the series are long they may 

 wind and twist so as to warrant bestowing such names as Maeandra 



cot 



Fig. 2. EXLAKGED LONGITUDINAL SECTION OF 



ASTREOIDES CALYCULARIS (PaLLAS). AftEU 



Lacaze-Duthiees. te, tentacles ; oe, oeso- 



PHAGCS ; mc, MESENTERY ; loC, MESENTERIC 



POUCHES ; coe, coenosarc ; spt, septum ; col, 



COLUMELLA. 



