120 



POPULAE ILLUSTRATIONS OP 



the plate, is a necessity of its existence, for the Coral is itself 

 brittle, and were the branches thinner they would inevitably be 

 broken by the waves. Observe that the exposed parts show 

 no pits or depression the surface being perfectly smooth. The 

 coenosarc is whitish in colour, and the polyps are milk white, and 

 nearly transparent. Its growth is slow it seldom is longer than 

 one foot, and this requires six or seven years to reach. 

 . The best Coral is found in the shallowest waters ; but it is found 

 as deep as 100 fathoms. Its ratio of growth is that of its depth. 

 Thus, it will increase in size a foot in eight years, in shallow water, 

 with a hot sun ; but it will take thirty years to reach that size at 

 100 fathoms. It varies in colour from yellow to a rich red. Dealers 

 recognise at least a dozen varieties. The hardest and most brilliant 

 in colour being the most prized. The same ground in the Coral 

 fisheries, as they are termed, is only dredged once in ten years, and 

 then in the rudest manner, by dragging a net over the bottom, and 

 thus getting what they can. 



Still another Alcyonarian polyp demands our attention. It is that 

 which forms the beautiful " Organ Pipe" Coral, a figure of which is 

 seen at Fig. 161 (frontispiece). There is a peculiarity about this 

 form, which leads us to the next group, inasmuch as although it 

 is one of the Alcyonaria, with eight tentacles, yet the corallite is 

 secreted upon the "tissue" or " sclero-dermic " plan, while all the 

 others of the family form their skeletons upon the "foot" or 

 " sclero-basic " system. 



We shall see that the first group of Corals, including all the reef 

 builders, secrete their skeletons on to former plan. 



The " Organ Pipe " is a very inter- 

 esting Coral. Only the polyps in the 

 top platform, as seen in the figure, are 

 alive as, in fact, I have before 

 noticed is the case in all Corals. The 

 polyp here has partially the power of 

 withdrawing itself into a calcareous 

 tube hence the name of the genus 

 Tubipora. They are of a beautiful 

 grass-green or violet colour, which 

 contrasts finely with the rich bright 

 crimson red of the Coral. Its mode 

 of reproduction is characteristic and 



/v> ,1 , i 



poiyp-c c c c, edges of platforms cut sufficiently curious to merit a short 



de8cri P^ on ' Fi ' 172 represents an 

 enlarged figure of one of the tubes and 

 its polyp. Fig. 161 (frontispiece). The polyp (a) is shown partially 



- 



Pipe Coral. a, polyp 6, tube with live 



