THE ACTINIANS OF PORTO RICO. 
373 
Fig. 20. Transverse section through a mesentery at the lower part of the stomodfeal region. The 
ciliated band, or reflected ectoderm, extends for some distance up each face of the mesentery, 
in some parts free and in others in union with the mesenterial tissues. On the lower left- 
hand side the intermediate tissue in section is overlying the cells of the ciliated band. 
Fig. 21. Transverse section through the free edge of a mesentery below the region at which the ciliated 
streak has terminated. The enlarged median part of the filament is altogether different in 
histological character from its condition in the uppermost part of its course; elongated 
granular gland cells and nematocysts are numerous. The mesenterial endoderm behind is 
also greatly swollen, and contains many deeply staining nutritive particles and gland cells. 
Fig. 22. Transverse section through the lower region of the mesentery, showing the last traces of the 
mesenterial filament. The magnification is much less than in the former figures. The 
mesenterial epithelium is greatly swollen, nearly surrounding the filament, and is strongly 
charged with nutritive particles 
Plate VI. 
Fig. 23. Isaurus duchcissaingi. Transverse section through the stomodfeal region of a polyp, showing 
the brachytype arrangement of the mesenteries and a large entocoelic outgrowth. At the 
slight magnification at which the section is drawn only the outlines of the walls can be 
represented, and the thin part of the mesenteries indicated by a simple line. 
Figs. 24, 25. Thick sections through two different polyps, representing the relationships of the smoot h 
and tubercular areas to the directive axis. The directive axis passes through the entoccele 
of the dorsal microdirectives and the ventral macrodirectives and includes the longer diameter 
of the stomodseum. In each figure the smooth area is at the upper right hand of the figure. 
The light areas represent the cut surface, the dark the tubercles projecting below. 
Plate VII. 
Fig. 26. Isaurus duchcissaingi. Tangential section through the ectoderm, showing the manner in which 
it is bi'oken up into subcubical blocks by the intrusion of the mesogloeal strands passing 
to the subcuticle. 
Fig. 27. Protopalythoa variabilis. Vertical section through the upper part of a strongly retracted polyp, 
including the tentacles, disk, and upper part of stomodseai wall. Only the details of the 
single mesoglceal sphincter muscle and foreign incrustations in the column-wall and disk 
are represented. 
Plate VIII. 
Fig. 28. Palythoa caribxa. Vertical section through the upper part of a strongly retracted polyp, repre- 
senting the single mesogloeal sphincter muscle. All the other structural details are omitted. 
Fig. 29. Asteractis expansa. Section through one-half of a polyp, showing the stomodseal wall, oral 
disk, tentacle, sphincter muscle (sp. ru. ), acrorhagus \ac. r.), parieto-basilar ( p.b.m . ) and 
basilar muscle ( b.m .), and inner and outer stomata. The mesentery is viewed on its 
exocoelic face. 
Fig. 30. Vertical section through the upper part of the column-wall, including an acrorhagus, the 
circumscribed endodermal sphincter muscle (sp. in.), and the basal part of a tentacle (<.). 
Fig. 31. Vertical section through a portion of the base, with a mesentery attached bearing the basilar 
muscle on each side. 
Plate IX. 
Fig. 32. Asteractis expansa. Transverse section of a sextant of a polyp through the lower part of the 
stomodfeal region. Four orders of mesenteries are represented. 
Fig. 33. Transverse section through part of the column-wall, including a verruca (ver. ) opposite a mesen- 
terial entocoele. 
Fig. 34. Bunodosoma granulifera. Vertical section through the upper part of the column-wall, showing 
the evaginations (ev.), acrorhagus (acr.), disk, and the circumscribed endodermal sphincter 
muscle. 
Plate X. 
Fig. 35. Bunodosoma granulifera. Transverse section of a retracted, strongly fluted tentacle. 
Fig. 36. Bunodosoma splierulata. Vertical section through the upper part of the column-wall, including 
an evagination (ev.), acrorhagus, and tentacle (cut obliquely), and showing the small 
pedunculated, circumscribed endodermal sphincter muscle. 
Fig. 37. Vertical section through a portion of the base, showing the basilar muscle on each side of a 
mesentery. 
Fig. 38. Transverse section through a mesenterial filament of the third cycle of mesenteries. 
