92 



INVEETrBRATE ANIMALS. 



and the polype-bearing fringes are ccmsiderably Linger, giving the 

 whole organism veiy much the ajipearance of a feather. In Vere- 

 tillum (fig. .53) the upper part of the colony is short and club-shaped, 

 and bears the polypes all round its circumference. 



Another fimily of the A/ri/onarlic is represented by the so-called 

 "Organ-jjijie conils," of which l\ihipora musica is a well-known ex- 

 ample (fig. 5.5). In this thei'e is a well-developed sclerodermic coral 

 consisting of ininierous cylindrical tubes, which are not divided by 

 vertic^J partitions (septa), b>it which are connected by strong trans- 

 verse jilates. The coi-al is bright red in colnur, and the polypes are 

 usually bi-ight green. In its minute structure, the corallum is com- 

 posed of microscopic sj)icules fused together. 



Fig. 55. — A, Pnrfion ftf tlie cor.iTIniii fi^ Tuliif^nra 'iiuisic<i, of tlio natural .size, sliowitig 

 tlie tiilnil;ir CMrallitcs ami tiwiT c^uinecting flours ; li, Pttlype of the sauie, gve;ltly 

 eiilavgtd, showing the liioutii and tentacles. 



The best known grou]), however, of the Alcyonaria is that fpf the 

 Gorr/iiiudii;, represented by the Sea-shrubs, Fan-coraLs, and the Red 

 ( 'oral of commerce. A few of the members of this family are British, 

 but they attidn their ma.ximum in point of size and numbers in the 

 seas of the tropics. In all the GorgimidtL' the organism consists of a 

 composite structure made up of muuerous polypes miited by a com- 

 mon Hesh or cieno.sjirc (tig. 5(1, B), the whole supported by a central 

 branched axis or coral. The coral v;iries in composition, being some- 

 times calcareous — ,is in lied ( 'ural — sometimes horny, ami sometimes 

 partly horny and p.artJy calc-ireous, as in [sis. In all cases, however, 

 the cor.iliuni difieis altogether from the sclerodermic coralbnn, which 

 has been described as so characteristic of the reef-building (Virals. 

 Tlie coral in the jiresent instance is always what is cilled "sclero- 

 b:isic" — that is to say, it always forms an internal axis, covered by 

 the cieiiosarc with the ]iolypes produced therefrom. It is therefore 



