CORALS. 



IIT 



related to the Actinaria of all the Actiiioids -which secrete lime is a beautiful 

 genus, M'hich bears the highly suggestive name of Fungia. It is the largest of 

 tlie solitary lime-secreting corals, and often reaches a diameter of from six to 

 eight inches. It is disk-shaped, with a large number of radiating partitions, or 

 sejita, which extend from the centre of the disk to a j)eriphery not bounded by a 

 vertical wall. The tentacles are not placed in a circle around the perijihery of 

 tlie disk, but are found irregularly disposed over its whole upper surface. Fungia, 

 in its adult condition, is not attached to the ground, but lies in the coral lagoons in 

 ratlicr sheltered ]>laces. In tlie younger stages, however, of its develojiment it is a 

 fixed form, aiul passes, according to Semper, through a larval condition com])arable 

 to the strobila of the Discophora, exhibiting a true alternation of generation. Repro- 

 duction also takes place in Fungia by fission and gemmation. The larger species 

 of the genus are found in the Pacific and Indian oceans. A small species, Fungia 

 si/mmetrica, was dredged by Pourtales, and afterwards by Mr. Agassiz in the "Blake," 

 in the depths of the Straits of Florida and the Caribbean Sea. 



There are several very fragile compound corals which in their young conditions 

 resemble Fungia, and which on that account naturally come in the neighborhood of 

 this genus. One of these, called Mgcedium, is one of the most common corals in 

 the sheltered lagoons of the Bermudas and along the Florida reefs. Mgcedium 

 fragile, called in the Bermudas the Shield Coral, has a thin, fragile disk, easily broken, 

 which hangs to the submarine cliffs a little below low-water mark. This disk has 

 a chocolate-brown color, which bleaches, as do most coral skeletons, into a beautiful 

 white. Upon the upper side of the disk we find two kinds of coral animals. One 

 of these is centrally placed, and is the mother of the colony, or the parent from 

 which the others have formed by a budding. The remaining individuals are smaller 

 than the central, around which they are arranged in concentric circles, which increase 

 in number with the diameter of the disk upon which they are formed. It will, there- 

 fore, be seen that we have in Mgcedium two kinds of individuals, a single, large 

 central animal, which is the oldest in the colony, and many smaller, which it may 

 at once be said are formed by budding from the original. Nothing is yet known 

 of a reproduction in Mgcedium by self-division or by the deposition of ova, although 

 there is every reason to suspect that both of these methods of formation of new 

 colonies really exist. 



One of the most common genera of Actinoid corals is called Madreporu. Although 

 rarely, if ever, found as far north as the Bermuda gi-oup of islands, it is one of the 

 most common of the reef-builders, and especially near the western termhiation of the 

 Florida Keys it forms great banks miles in extent, whose ujjper surface rises to within 

 a few inches of the low-water level. 



One of the most abundant species of Madrepore is M. cerviconiis, a branching 

 species, which sometimes attains a large size. The difiiculty of comprehending the 

 structure of Madreporu comes from the fact that in each branch of one of the dendritic 

 species, as cervicornis, we have a large number of different individuals arising from a 

 common axis. If we take a terminal fragment of such a branch,, we can see that its 

 very tip is formed by a small rounded body of calcareous nature, in the interior 

 of which there are radiating partitions jiassing from centre to circumference, as in the 

 genus Fungia. The jieripheral ends of all these septa are bounded by a calcareous 

 wall connecting them all, which is absent in the last-named genus. If we study care- 

 fully the slight excrescences upon the sides of the branch, we find that although 



