MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 543 



MADEEPORA MURICATA Linnseus. 

 (PK I-III, figs. 1-27.) 



External characters. — Madrepores are everywhere abundant on the reefs around Jamaica, and 

 in other places on tlie sea floor, where conditions are favorable. The three foi-nis, or rather 

 groups of forms, recognized bj' Brook (189.3), and by practically all writers, are always readily 

 distinguishable, and are often found living together. Broadly speaking, they are as follows: 



1. The flabellate or palmate colonies, with large, flat or concave fronds, usually several 

 radiating from an incrusting l)ase: Forma jxtlmata. 



2. .Much-bi'anched colonies, several branches radiating obliquely from a common center, 

 main branches about 1.7 cm. thick at the base: Forma prolif era. 



'i. Large, more erect colonies than the last, less branched except toward the periphery, 

 stem and l)ranches much stouter, from 2 to 4 cm. thick: Forma cervicornls. 



In Jamaican waters the three typical forms are distributed as follows: Thin flabellate colonies 

 occur ill tlie shallowest regions, ])eginning at a depth .sufiicient to permit of their extremities 

 being expo.sed during the lowest tides, and extending downward to several fathoms. Beyond a 

 fathom or two these are for the most part replaced by the palmate variety, in which the proximal 

 part of each division becomes very thick and may be nearly rounded, the distal region only being- 

 thin and flattened. Associated with the flabellate and palmate colonies may be the proUfera form, 

 but this rarely reaches so near the surface ^ii pahnata. At depths of from two to three fathoms 

 the true cervlcornin commences, and often forms dense thickets. 



Whei'e a properly equipped lalioratorj^ is not established, some difficulty is experienced in 

 securing the polyps in a fully expanded state under conditions suitable for observation. In situ 

 they may soiiietimes be seen fully expanded, but, upon breaking off a fragment for closer 

 examination, the shock causes the polyps throughout the branch to retract. The axial polyps are 

 then retracted to such a degree that no trace of them is distinguishable, and the radial polyps 

 display only the tips of a few tentacles just within the calice. Brought into the laboratory in 

 this condition, and placed in the shade, they usually expand a little farther, so that the tentacles 

 of the i-adial polyps can be counted and their genei'al arrangement made out. At night they 

 expand to their full degree. 



The whole of the living .surface of a colon}- is covered with a stnooth delicate tissue, which 

 adheres clo.sely to the skeleton over the costss and echinulations, but is free over the intervening 

 canal spaces. Microscopic examination reveals that the superficial covering of the skeleton is 

 for the most part double; an inner wall adheres directly to the skeleton, while the outer is more 

 or less free from it (PI. I, figs. 2-6). On full expansion of the polyps the outer fleshy covering 

 becomes slightly distended, and on retraction or preservation is partly depressed within the 

 intercostal grooves. The superficial tissues are continuous throughout, without any grooves 

 limiting one polyp from another. Over the greater part of a colonj' the polyps are clo.sely 

 arranged, separated by a very limited coenosarcal area; in the older regions the polyps are more 

 distant than in growing parts. When the polyps are expanded the superficial covei'ing of 

 the colony passes uninterruptedly into the column wall of the polyp, and the two are seen to be 

 direct continuations of one another (fig. \a). 



The polyps found at the apex of branches differ so markedly from the lateral or radial 

 polyps that it will be neces.sary to describe the two separately. The apical pol^'ps are difficult to 

 obtain in a fully expanded condition for ob.servation ; usually they are I'etracted within the calice 

 to such a degree that no trace of the tentacles is presented. On favorable occasions, however, 

 the polyps extend beyond the coralhun for a distance of 3 mm., when they are seen to be 

 perfectly radial in their outward symmetr}-, and of the same diameter as the aperture of the 

 corallite lieyond which they protrude. The column wall is cylindrical, smooth, colorless, and so 

 transparent as to permit of th(^ internal mesenteries and short stomoda-um being .seen. At the 

 inner margin of the apex of the corallite the column wall of the pol^^p is in continuity with the 

 cceno.sarc, and distallv it passes uninterruptedly into the tentacles and disk. 



