232 



THE OCEAN WORLD. 



well-developed polyps, and particularly those with branching extre- 

 mities, in which this phenomenon is produced. The new beings 

 resemble little white points pierced with a central orifice. Aided by 

 the microscope, we discover that this white point is starred with 

 radiating white lines, the edge of the orifice bearing eight distinctiy- 

 to-be-traced indentations. All these organs are enlarged step by 

 step until the young animal has attained the shrub-like or branched 

 aspect which belongs to the compound polypidom. The tube is 

 branching, and the orifices from which the polyps expand become 

 dilated into cup-like cells. 



The coral of commerce, so beautiful and so appreciated by lovers 



of bijouterie, is the polypidom. 

 It is cylindrical, much channeled 

 on the surface, the lines usually 

 parallel to the axis of the cylinder, 

 the depressions sometimes corres- 

 ponding to the body of the animal. 

 If the transverse section of a poly- 

 pidom be examined, it is found to 

 be regularly festooned on its cir- 

 cumference. Towards its centre 

 certain sinuosities appear, some- 

 times crossing, sometimes trigonal, 

 sometimes in irregular lines, and 

 in the remaining mass are reddish 

 folds alternating with brighter 

 spaces which radiate from the 

 centre towards the circumference 

 (Fig. 89). In the section of a very 



red coral, it will be observed that the colour is not equally distributed, 

 but is separated into zones more or less deep in colour, containing 

 very thin preparations which crack, not irregularly, but parallel to 

 the edge of the plate, and in such a manner as to reproduce the 

 festoons on the circumference. From this it may be deduced that 

 the stem increases by concentric layers being deposited, which 

 mould themselves one upon the other. In the mass of coral 

 certain small bodies (spicules) occur, with irregular asperities, much 

 redder than the tissue into which they are plunged. These are much 

 more numerous in the red than in the light band, and they necessarily 

 give more colour to the general tint. 



To the mode of reproduction in the coral polyps, so well described 

 by Lacaze-Duthiers, we can only devote a few lines. Sometimes, 



Fig. 89. Section of a Branch of Coral. 

 (Lacaze-Duthiers.) 



