742 PROCEEDINGS OF THE AMERICAN ACADEMY. 



colony was 110 cm. high with 250 terminal branches. A third meas- 

 ured 200 cm. in height and had 300 terminal branches. These three, 

 taken from one place, are representative of the forms inside the outer 

 reefs. On the outer reefs, forms 225 cm. high have been found. In 

 the first colony (90 cm. high) the diameters of the stems were measured. 

 Half way between the ground and the tips, with the polyps fully 

 expanded, the branches were 4 cm. in diameter; at the base, 5 cm., 

 and near the tip, a little more than 3 cm. After the polyps were fully 

 contracted, the measurements were 1.5 cm. for the base, and .5 cm. 

 for the tip. 



A trans^'erse section of a branch, or whip (Plate 1, Fig. 1), shows 

 the structure. In common with that of the branches of Gorgonacea 

 generally, there are recognizable three zones : a central axis of skeletal 

 material {ax.), a fleshy enveloping layer, — the coenenchyma, — and a 

 zone of polyps. The polyps can completely retract into spaces in 

 the coenenchyma, whereupon two zones only are evident. The horny 

 axis is very hard at the base but quite soft at the tip of the branches 

 and, except at the basal end, is -very flexible. To the naked eye, it is 

 composed of two parts, a central, soft marrow, light in color (white 

 in the figure), and an outer, harder, brown or black tubular shaft or 

 cortex. The marrow has nearly the same thickness in all parts of the 

 colony.^ While its diameter is sometimes slightly smaller at the tip, 

 it is not always so. Its variations are not wholly dependent on age, 

 for it is slightly larger or smaller in parts of the stem and these parts 

 occur irregularly. It is composed of a number of chambers filled with 

 loosely branching threads (compare Plate 4, Fig. 58), and having walls 

 of horny material, the chambeis being generally arranged one above 

 the other (Plate 4, Fig. 57, vied. ax.). The loosely branching threads 

 in the chambers are not shown in this figure, but are seen in the small 

 chamber of the axis-cortex shown in Figure 58. The walls of the 

 medullary chambers are very thin. Those of the axis-cortex chambers 

 are very thia at the tip of a branch, while at the base they are very 

 thick and hard. This is due to the fact that while the marrow cham- 

 bers are laid down axially (i. e., at the end of the axis) in the branch, 

 the cortex grows radially. The latter is composed of smaller cham- 

 bers, which in longitudinal sections appear crescent shaped (Fig. 57, 

 dx. ax.). Not only is the cavity smaller, but the walls are thicker 

 than those of the marrow. The first crescents laid down are adjacent 

 to the marrow and very short, but as the axis-cortex increases in 



2 This cortex of the axis will bo called axis-cortex to distinguish it from 

 the more superficial coenenchymal cortex. 



