ALCYONARIAN CORALS 115 



in the direction of the platform next below it, and then it 

 may be called a funnel-shaped or " infundibuliform " tabula. 



In many tubes, however, it is found that an infundibuli- 

 form tabula, instead of ending blindh^ expands again to 

 form an inverted funnel, the mouth of which is on a level 

 with the next platform. Thus we find within the tube an 

 inner tube, which contracts to a capillary size in the middle, 

 a structure which is obviously of the same nature, but 

 utterly unlike what is usually called a tabula in works on 

 corals. The interpretation of these different forms of 

 tabulae in Tubipora has been given elsewhere ; ^ but it is 

 important to note that the character of the tabulae varies 

 enormously, not only in the tubes of a single specimen, but 

 also in the different regions of a single tube, and it is there- 

 fore quite useless as a character for specific distinctions. 



The genus Tubipora is one of the many genera of corals 

 in which the question of species is one of extraordinary 

 difficulty. 



The lumps of this coral that are to be seen in museums in 

 this country differ from one another in shape, in the size of 

 the tubes, in the distance separating the platforms, and to 

 some extent in the shade of red colour of the coral substance. 

 All these characters, however, are so variable, so dependent 

 upon the characters of the environment in which the corals 

 grow, that any system of species founded upon them would 

 fail on account of an indefinite number of intermediate 

 varieties. On the shore of the Island of Celebes the author 

 took the opportunity' to collect and examine many hundreds 

 of specimens that had been washed up by the sea and many 

 scores of specimens alive on the coral reefs, and came to the 

 conclusion that almost every variety that is known could 

 be found on that one shore, and that there is complete 

 continuity between one extreme variety and another. This 

 does not entirely dispose of the question of specific grouping, 

 as other characters may yet be discovered which do not 

 exhibit the same degree of individual variability, but it 



^ S. J. Hickson, Quart. Joitrn. Micr. Sci . xxiii., 1883. These curious 

 infundibuliform tabulae appear to ha\-e been first noticed by Ellis and 

 Solander, Zoophytes, Plate 27, 1786. 



