LECTURE VII. 



lated and radiated structure which we recognise in the enduring 

 support of the large Fungice and in the polype cells of the skeletons 

 of the CaryophillecB, MadreporcB, &c. 



The species of jjolypes which take the most important share in the 

 fabrication of the coral islands and reefs, belong to the present group, 

 and have esentially the organisation of the sea-anemony, which has 

 just been described. 



To the eight-armed division of the Anthozoic Polypes belong those 

 species which have an internal ramified calcareous or jointed axis, as 

 the red coral polype (^fig. 46. c), the gorgonia, and the isis. To this 

 division likewise belongs our common Alcyonium, or dead-man's- 

 toes, in which the hard axis is wanting ; and the phosphorescent Sea- 

 pens_, the Veretillum, and other Pennatulidce, in which it is in de- 

 tached pieces. 



These are all examples of compound Anthozoa, differing from the 

 compound hydriform polypes in having an internal instead of an 

 external skeleton. The body of each polype (^fig. 47.) is relatively 



longer than in the Actiniae ; the pre- 

 hensile tentacles (a, a) are broad and 

 pectinated : at the centre of their base 

 is situated the mouth (b), which leads 

 to a straight membranous alimentary 

 cavity, fixed by vertical septa {d, d) 

 to the external integument ; which 

 septa are continued down the general 

 visceral cavity. The digestive canal 

 communicates with this cavity by a 

 small orifice (e) at its inferior part. 

 Ovaria and tortuous filamentary se- 

 creting organs (f) analogous to the 

 testes in the Actinia, are developed 

 in the common visceral cavity, A 

 delicate network of vessels conveys 

 the nutrient fluid to the common con- 

 necting parenchyma of the entire 

 compound animal. 

 This parenchyma is strengthened in our common Alcyonium by 

 numerous minute calcareous spiculas. Analogous spiculae, but of 

 varying and characteristic forms, strengthen likewise the animal 

 crust of the red corals, jointed corals, and Gorgonise ; but to these is 

 superadded the internal branched axis, which, according to its com- 

 position and structure, characterises the diff'erent genera of this group. 

 In one genus, the external position of the skeleton which characterises 

 the hydriform compound polypes is repeated, viz. in the Tuhipora 



Polype of the red coral. 



