45^ TAHITI. 



rounded by a ring of five, six, or seven dactylopores, as shown 

 in the accompanying figure, where the circular groups of minute 

 pores are seen scattered over the coral surface. 



The second figure shows, much enlarged, a single system of 

 polyps belonging to one of these pore systems, as it appears 

 when the polyps are fully protruded from their pores and 

 expanded. Beneath is seen shaded dark part of the canal 

 mesh-work, which maintains the general circulation of the 

 colony. From this stands up in the centre, the short and 

 stout gastrozooid with its four tentacles, and dark stomach 

 cavity seen through the walls of its body, and its mouth at its 

 summit. Around are grouped five dactylozooids, each with 

 many tentacles, but without any mouth or stomach. One of 

 the dactylozooids is seen bending over to feed the gastrozooid 

 of the system. 



Marvellous as is the completeness in the division of labour 

 in the Millepora Colony, this is far surpassed in the case of the 

 Stylasteridce, another family of stony corals, which, as I found 

 to my astonishment, is also like the family Mi/kporidcr, 

 Hydroid in structure. 



In the Stylasteridcc there is a canal network and common 

 circulation in each colony essentially similar to that in the 

 MilleporidiC. Two kinds of polyps also, mouth-bearing and 

 mouthless, are present. The dactylozooids are, however, en- 

 tirely devoid of tentacles, and are reduced to simple long 

 tapering bodies, just like the tentacles of Sea Anemones in 

 appearance, and performing the same functions. The gastro- 

 zooids alone bear tentacles around their mouths, and in some 

 genera even they have lost their tentacles, and the entire 

 colony is thus devoid of these appendages. In some genera 

 there are two kinds of dactylozooids, smaller and larger, the 

 latter evidently intended to be enabled to better catch food by 

 means of their long reach, the former probably to deliver the 

 food so caught to the mouth-bearing polyp. 



The accompanying woodcut shows the principal living struc- 

 tures as they exist in one of the more simple genera of the 

 Stylas/eridce, namely, the genus Errina. The various com- 

 ponent structures are displayed as they are seen when the 

 calcareous skeleton of the coral has been removed by the 

 action of acids, and the remaining soft tissues have been cut 

 through in a direction at right angles to the surface of the 

 coral. The calcareous style is introduced into the drawing in 

 order to show its relation to the gastrozooid. In the case of 

 the Alilleporidie, the mode of reproduction is not known ; it is 

 possible that they produce free-swimming Mediiscc. In that of 

 the Sty/asteridtc, on the other hand, the process is well under- 



