744 PROCEEDINGS OF THE AMERICAN ACADEMY. 



in a close mass. The diagrammatic nature of Figure 1 does not per- 

 mit one to show the closeness of the interlocking of these spicules. 



The outer region of the coenenchyma is a thick zone with polyp 

 chambers (cam. pyp.), into which the polyps can completely retract. 

 These chambers communicate with each other Iw a greatly branched 

 system of small canals (can.). These canals are represented in only 

 one half of Figure 1 (Plate 1). The actual canals are much more 

 numerous and are more complexly branched than the diagram shows. 

 Between the chambers white spindle-shaped and spiny spicules 

 (Fig. B, 1-4), longer than the purple ones of the inner region, are 

 found (spc). Some of the deeper of these may be purple. Indeed 

 there is considerable variation in both color and form of the spicules 

 of different colonies and even of the same colony. These spicules 

 have been described and figured by Wright and Studer ('89), by Har- 

 gitt and Rogers (:01) and by Verrill (:07). Figure B gives the rela- 

 tive proportions in size, as well as the differences in shape for the 

 spicules of both the inner and outer regions of the coenenchyma. 

 Figure B, 5-7, presents spicules of different shapes found near the long 

 canals, where they are often locked together. In Figure B, 1, 2, 

 are seen long white forms from the outer part, and in Figure B, 3, 4, 

 spicules from the deeper part of that region. 



The polyp-zone consists of the exposed part of the polyps or antho- 

 codia (Fig. 1, a-y). These when expanded are cylindrical. The 

 mouth is oval and the eight tentacles of the crown stand at right 

 angles to the column. The tentacles are conical, relativel}^ long when 

 fully expanded, and carry ten to twelve pairs of conical pinnae, ar- 

 ranged in two longitudinal lines, one on either side. No spicules are 

 found in the polyps. 



The anthocodia are brown and, when expanded, give the colony 

 its prevailing color, which is caused by the presence of the Zooxan- 

 thellae (Plate 2, Figs. 20, 21, zox.) that crowd the endoderm cells and 

 give a lighter or darker brown color in accordance with the degree 

 of the animal's contraction. A little magnification shows that each 

 disk is white and also that along the eight longitudinal lines corre- 

 sponding to the union of the mesenteries with the body wall the color 

 is white. The white appearance in both cases is due to the absence 

 of these algae. The color of the coenenchyma between the anthocodia 

 is distinctly white because of the absence of Zooxanthellae near the 

 surface and the presence of white spicules. 



The wall of the column of the anthocodium (Plate 1, Fig. 1, |S) 

 merges into that of the somewhat larger chamber in the coenenchyma 



