50 CORALS 



always constant, and, in some forms of Galaxea even, some 

 of the buds may arise from the outer wall of the calyx, a form 

 of gemmation that is called " Epicalicinal " or " Epithecal." 



\Mien the Galaxea colony is alive, the soft flesh covers 

 the whole surface of the colony as with a mantle. It is not 

 locked into the corallum, as it is in the Perforate corals, by 

 a system of canals perforating the subjacent hard parts. 

 When the colony is killed, therefore, parts of the tissues as 

 they become hardened are often detached, or may be 

 detached with a little manipulation with needles, showing 

 that this flesh is entirely superficial. 



The polyps show a crow'n of twenty-four simple tentacles 

 surrounding a centrally placed mouth, and there are twenty- 

 four mesenteries, of which two pairs are directive mesenteries, 

 in the fully developed condition. 



The colour of the living polyps probably varies in 

 different localities, but in a specimen observed by the author 

 on the reefs of Celebes they were of a bright emerald green 

 colour, the expanded colony, as seen through the clear water 

 in the sunshine, being one of the most brilliant of the many 

 beautiful corals of the locality. 



Favia. — The second type which may be taken to illus- 

 trate the structure of the Astraeid corals is a genus which 

 is, perhaps, most correctly called Favia (Fig. 17). But in 

 this case, as in many others of the same family, the student 

 will find great difficulty in coming to a definite conclusion 

 as to the correct generic name of a specimen owing to the 

 differences of opinion expressed by those whose detailed 

 study of Madreporarian structure has given them the right 

 to be regarded as authorities on the subject. Apart from 

 questions of the law of priority in nomenclature, there is 

 the difficulty in this group arising from the fact that there 

 is so much variation in the species, and there are so many 

 closely related genera that many perplexing examples occur 

 of intermediate or overlapping species and genera. The 

 consequence is that the old genera have been split into 

 several new genera and the new genera reunited under the 

 old generic name in a way that has made it very difficult 

 to maintain an accepted or acceptable nomenclature. 



