178 CORALS 



tlie grie\-()us blunck'i" of supposing it to be the young stage 

 of the true Red coral {CoraUiuni nohilc) ; but it \\-as the dis- 

 tinguished French naturahst Dujardin who, having observed 

 in 1841 a " substance glutineuse " in the chambers, placed 

 it tentatively among the Rhizopoda. 



The genus has since been thoroughly investigated by 

 Mobius, Merkel, and other investigators, and its place in 

 the group of the Foraminifera has been firmly established. 



It is not necessary to describe in detail the structure 

 and life-history of the organisms that form the shells and 

 corals of the Foraminifera, but it may be said that by no 

 extension of the meaning of the words can they be called 

 " polyps " or " zooids." They consist of a mass of the 

 granular semi-fluid living substance called Protoplasm 

 and show no differentiation into cells and no structural 

 organs. There are no tentacles, no mouth, and no defined 

 digestive canal or cavity. Embedded in the substance of 

 the protoplasm there is a nucleus or, in some stages of the 

 life-history, several nuclei. 



The food of the Poh'trema is obtained by a network 

 of very delicate but anastomosing protoplasmic filaments 

 which project from the ends of the branches. These fila- 

 ments are called the Pseudopodia. 



\Mien the dried calcareous structure of the Polytrema 

 (Fig. 87) is examined carefully with a lens, the surface of the 

 base and of the branches is seen to be perforated by a 

 number of minute holes. There are two kinds of holes, the 

 larger kind called the " pillar pores " and the far more 

 numerous smaller kind called the " foramina " (Fig. d>d>, A). 

 The sub.stance of the coral below the surface is built up by 

 the perforated calcareous walls of a number of chambers 

 which are arranged more or less concentrically at the base, 

 but are much more irregular in the stem and branches. More- 

 over, in the axis of the stem and branches there is a tendency 

 for the cavities of the chambers to fuse so as to form an 

 irregular but continuous lumen, the branches thus becoming 

 hollow or tubular. 



This lumen ends at the extremity of each of the branches 

 in a large irregularly round aperture, and projecting from the 



