528 A NATURALIST ON THE " CHALLENGER, 



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when the polyps are fully protruded from their pores and ex- 

 panded. 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 with- 

 out 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 Mille_poridw, Hydroid 

 in structure. 



In the Stylasteridce there is a canal network and common 

 circulation in each colony essentially similar to that in the 

 Mill evor idee. 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 ap- 

 pearance, and performing the same functions. The gastrozooids 

 alone bear tentacles round 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 

 Stylasteridce, 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 Millevoridm, 

 the mode of reproduction is not known ; it is possible that they 



