MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 559 



EiR'b colonj- is usually divisible into smaller subcolonies, in which a certain numner of the 

 polyps are .still united one with another b\- the column wall. In any distinct subcolony rarely 

 more than four or five pol3'ps are united, branching- at an angle varying from nearly a right angle 

 to about 45°. Sometimes a single polyp may be disconnected from all the others, or only two or 

 three ma\' be in union. All stages in the formation of subcolonies, by the disappearance of the 

 intervening portion of the soft tissues, are presented. Daring the process the proximal part 

 of the column wall of two united polyps becomes constricted more and more, and finally the last 

 connecting strand l)reaks down, and the polyps are completely isolated. The separation of 

 individual jjolyps is more f rc([uent in some of the humbler, bushy colonies, while other colonies are 

 met with in which all the polyps are still united, no subcolonies being formed, or verj- sparsely. 



The part of the skeleton exposed by the withdrawal of the lower perithecal portion of 

 the column wall and skeletotrophic tissues is at first clean and white, and covered with a very 

 thin epitheca; l)ut worm tub s, algse, etc., from the older, dead parts of the colony soon encroach 

 upon it. 



The column wall is cylindrical, and extends downward over the outside of the skeleton for a 

 varying distance in different polyps, but rare! 3' exceeding 5 mm. from the thecal edge. The surface 

 is smooth and semitransparent, and is very distinctlj' ridged and grooved throughout its extent, 

 the ridges corresponding with the costre and the grooves with the internal attachment of the mesen- 

 terial continuations. The mesenteries seem to extend the full length of the column, but sections 

 reveal that toward the lower extremitj^ some become free from their inner attachment, or may dis- 

 appear altogether (figs. 51, 54). When the polyps are expanded to their fidl extent, the column, 

 tentacles, and disk become removed some distance from the underl3'ing skeleton, and the columnar 

 ridges and grooves are not veiy pronounced. The column may extend upward as much as 4 mm. 

 bevond the theca, and the disk, becoming conical, may add another 4 mm. On full retraction the 

 tissues adhere very closelv to the corallum, following its elevations and depressions; above, the 

 column wall is overfolded, so as to cover the tentacles and greater pai't of the disk. On partial 

 retraction the column wall is sometimes constricted inacircular manner, just below the tentacular 

 zone. The lower, terminal edge of the column of the lowest polj^p in a subcolony is very sharply 

 defined, and the upper passes directl\' into the tentacles. 



The tentacles are in three or four cycles, but be3'ond the first cvcle of six the arrangement 

 is difficult to determine, as but small variations in size are exhibited, and the C3'cles are closely 

 arranged. The general appearance is that of two alternating C3'cles of nearl3' equal size. The 

 total number of tentacles varies from twent3'-four to thirty-six; thirty and thirty-four are 

 most frequentl3^ counted. 



All the tentacles are rather broad at the base, and narrow towards the apex, which is slightly 

 swollen or knobbed. In the expanded condition the organs are usually overhanging, often one 

 cycle to a greater extent than the other. Sometimes the members of the outer C3'cle may be 

 reflected to such a degree as to be opposed to the column wall, while those of the inner C3'cle 

 remain erect. Occasionally^ the tentacles ma3^ be shorter and more swollen proximallv, as in the 

 figure given In' von Heider of C. ce-ytitum (1881), but generalh' the\^ are long and narrow. In 

 one or two instances a tentacle with a bifurcated apex has occurred, each half provided with a 

 swollen tip. 



The tentacular walls are verv delicate and transparent on full distention, bearing minute 

 white tubercles over the whole surface. Like the apical swelling, these are onlv thickenings 

 of the ectoderm, and on microscopic examination ai-e seen to be batteries of stinging cells. The 

 tentacles correspond in position with the septa and costiv, which are easilv seen through the semi- 

 transparent tissues; the inner tentacles are placed over the larger septa, and the outer C3'cle over 

 the alternating smaller septa. The tentacular ape?: has considerable adhesive power, holding 

 on to anv body brought in contact with it; the distal part of the stem also tends to fold round 

 an3' object. The length of the innermost tentacles during full extension ma3' be as much as tj mm. 



The disk is smooth, circular, 2 or 3 nmi. in diameter, and radiately grooved in correspondence 

 with the internal complete mesenteries. In retraction it is depressed for some distance within 

 the calice, assuming a cup shape; but sometimes the pei'istomial region is elevated. The 



