192 CORALS 



In external form it might be mistaken for a Millepora 

 or a Heteropora, as it consists of a broad base from which 

 a number of short C34indrical or flattened dichotomously 

 divided branches rise to a height of an inch or more. 



When fresh the white coral substance is covered by a 

 white or yellow film of sponge substance and spicules, but 

 this disappears when it is dead and macerated. 



The dried coral may be distinguished from other corals 

 by its spongy texture and the absence of any regular pores 

 or channels, but more particularly by the character of the 

 surface, which is provided with a number of small pointed 

 vertical pillars like a palisade. Among these pillars there 

 may be found some of the characteristic forked calcareous 

 spicules which are suflicient by themselves to suggest to 

 the naturalist that the structure must have been formed by 

 a sponge ; but a careful study of the coral with a lens shows 

 that the pillars at the surface and the subjacent structures 

 have been formed by the growth and fusion of these spicules. 



Annelid Worm Tubes 



In the examination of corals of various kinds the 

 naturalist frequently finds a number of long, straight, coiled, 

 or twisted calcareous tubes which have been formed by 

 different kinds of Polychaet worms. 



In such a tangled mass of coral as that shown in the 

 illustration of Lophohelia (Fig. 5, p. 28) a number of such 

 tubes, distinguished by their smooth cylindrical contour 

 and the absence of septa, are invariably present. In Helio- 

 pora again the corallum is always perforated by small 

 tubes of the same kind (Fig. 52, p. 119). There are many 

 corals which possess some power of protecting themselves 

 from uninvited guests of this sort, but still it must be said 

 that most corals are liable to be penetrated by and frequently 

 distorted and disturbed in their normal manner of growth 

 by certain kinds of sedentary polychaet worms. 



The relation between the hosts and the guests in this 

 association may not be clearly understood. It is difficult 

 to believe that the coral hosts are ever seriously incon- 



