456 TAHITI. 



bud out before its predecessor was quiie free. The somewhat 

 cup-shaped buds, when set free, become, by the direction in 

 which future growth takes place, flat and disc-shaped, and 

 develop eggs, from which spring free-swimming larvoe, which 

 start fresh stocks. 



The mass of nurse stocks which I found was surrounded on 

 the reef by a group of fully-formed Fii?jgias of all sizes, 1 

 counted twenty in all. vSome six of these were small and still 

 showed the scar of attachment, which disappears in the process 

 of subsequent growth. 



A species of Milkpora {M. nodosa. Esper), is a very common 

 coral upon the Tahitian reefs. It forms irregular nodular 

 masses usually of small size, and often encrusts dead corals of 

 other species. The tips of the lobes of the living coral are of 

 a bright gamboge-yellow colour, which shades off into a 

 yellowish-brown on either side of the lobes. Mr. Murray 

 succeeded in getting the polyps of the coral to expand under 

 the microscope, and handed them over to me for examination. 

 I found them, as Agassiz had discovered long before, to be 

 Hydroids allied to the AIedi4sce and not to the Actinozoa and 

 Sea Anemones, like the majority of modern stony corals. I 

 studied the structure of the coral minutely.* 



The hard part of the coral or calcareous skeleton is finely 

 porous throughout, being excavated by a complex reticulation 

 of fine and tortuous canals which are in the freest possible 

 communication with one another. Within this porous mass at 

 its surface are excavated cylindrical holes or pores of two 

 sizes. 



The canal spaces in the skel ;ton are, when the coral is 

 living, filled by a network of liviig tissue made up of a mesh- 

 work of branching and commuiiicating tubes, which form a 

 canal system, by means of which a free circulation can pass 

 from one part of the coral to another. 



Two kinds of Polyps inhabit the pores described as existing 

 on the surface of the coral. The larger pores are occupied by 

 short stout cylindrical polyps which have each four tentacles 

 and a mouth and stomach, and which are hence termed " Gas- 

 trozooidsj" whilst their pores are termed " GastroporesT The 

 smaller pores shelter each a very different kind of polyp, which 

 has a long and slender sinuous body provided with numerous 

 tentacles, and devoid of any mouth or stomach ; this latter form 

 of polyp, because its function is merely to catch food, is called 

 a '■'• Dactylozooid,''' and its pore a '■'■ DadyloporeP 



* For further details, see H. N. Mosclej-, "On the Structure of a Species 

 of Millepora occurring at Tahiti." Phil. Trans. Roy. Soc, Vol. 167, 1877, 

 p. 117. 



