FORAMINIFERAN AND OTHER CORALS 193 



venienced by the worm guests. They may not grow into 

 exactly the same shapes as they would without them, but 

 they show no signs of reduced vigour or general health. 

 In some cases, such as that of Heliopora and Leucodora 

 (p. 119), the association appears to be constant, the Heliopora 

 always harbouring its Leucodora guests, but in others the 

 worms may or may not be present, and the corals without 

 the worms are apparently as healthy as those with them. 

 There is no reason, therefore, to suppose that the worms 

 in any way assist their coral hosts in the struggle for 

 existence. The association must be regarded as one of 

 commensalism, the host and guest feeding at the same 

 table, without injuring or benefiting each other. 



It does not seem to be a case of mutualism such as that 

 of Heteropsammia (p. 78) and the Sipunculid worm, in 

 which both the host and guest benefit by the association, 

 and more certainly it is not a case of parasitism. The 

 worm must not be branded with the stigma of a parasite. 



But although they are so often associated with corals 

 it must be remembered that the tubiculous worms are also 

 found in immense numbers living an independent life 

 attached to various kinds of solid objects. Every one must 

 be familiar with the little spiral tubes of Spirorbis attached 

 to the seaweed and stones that are washed up on the beach 

 and the larger meandering tubes of Serpula attached to 

 oyster shells. Not infrequently it is found that tubes of 

 Serpula will almost completely cover the shells on which 

 the}^ have settled, and sometimes they run over one another 

 in serpentine fashion to form lumps of intertwined calcareous 

 tubes several inches in diameter. 



It is perhaps stretching our definition of the word beyond 

 its legitimate boundaries to call such lumps " coral." It 

 would be better if they could always be called " worm tubes." 



But there is one of these Polychaet worms which forms 

 great masses composed of a lab3^rinth of small calcareous 

 tubes that are frequently many inches in diameter and 

 might readily be mistaken for a coral. 



The genus Filograna (Fig. 99) seems to have an almost 

 world-wide distribution in shallow water, and sometimes is 



o 



