CORALS AND CORAL~ANI .VIALS. 141 



of these rock-incrusting Nullipores being usually pink or lilac, they impart, where they are 

 abundantly developed, a very characteristic feature to the reef-scape. In the deeper rock-pools, 

 and on the sea-bottom generally, in the neighbourhood of the reefs, another generic form, 

 Halimeda, belonging to the same Nullipore tribe, is locally abundant. This type forms erect, 

 branching tufts, often several inches in length, of which the branchlets are composed of flattened, 

 irregularly polygonal, or more or less fan-shaped, calcareous disks, strung together, as it were, in 

 a moniliform or chain-like order. While growing, this Nullipore is a brilliant grass-green, but it 

 bleaches, when dead, to a pure white. The bleached discoidal segments of its disintegrated 

 fronds often occur in great abundance among the mixed calcareous components of reef-rocks 

 and coral sand. A familiar representative of this Nullipore family that abounds on the British 

 coast is known by the name of Corallina officinalis, so-called on account of its formerly supposed 

 valuable medicinal properties. Its elegantly divided fern-like fronds are composed of slender, 

 cylindrical, calcareous joints that vary through every shade of pink and lilac. 



Before entering upon a detailed description of the organic class which constitutes the 

 prime factor in the construction of all coral-reefs, a brief outline sketch of its leading modifi- 

 cations and limitations is desirable. The significance of all typical coral structures as the 

 skeletal elements of animals, essentially identical in aspect and organisation with ordinary 

 skeletonless polyps or sea-anemones, has been already indicated. Hence it is that all oi the 

 organisms, typified by the soft, askeletal, sea-anemones, and the skeleton- or coral-secreting 

 polyps, that enter into the composition of the living coral-reef are associated together by 

 naturalists into a single comprehensive animal group or sub-kingdom, upon which the title of 

 the Coelenterata has been conferred. The Ccelenterate, or polyp class, as, in non-technical lan- 

 guage, it may be more conveniently termed, contains, moreover, an infinity of forms that, 

 as it were, bridge over the hiatus between the solitary skeletonless sea-anemones and 

 those polyps which in their myriads represent the chief agents in the building up of 

 the massive reef. There are, in the first place, intermediate polyp species which, while not 

 possessing a definite skeleton or " corallum," as it is technically termed, have their tissues so 

 filled and strengthened with microscopic calcareous deposits or "spicules" that their sub- 

 stance is distinctly tough and coriaceous. This group is most prominently represented among 

 the constituent elements of the ccral-reef, by what are known as the Alcyonaria, having as 

 their type in European seas the so-called "Dead-men's fingers," Alcyoiiiuin digitatmn, com- 

 monly cast on the beach after storms, or obtainable with the dredge a little below low-water 

 mark. The extent to which these Alcyonarian polyps enter into the composition of a liv- 

 ing coral-reef is instructively illustrated by Plates XIX. and XX., wherein their flexible, 

 leather-like, coralla occupy the bulk of the reef-scape and may cover an area of many acres. 

 To a lesser degree, these Alcyonaria are represented in the greater number of the photographic 

 reef-views that illustrate this volume. A noteworth}' structural peculiarity of all the polyps 



