CARPENTER. — FEEDING REACTIONS OF THE ROSE CORAL. 151 



like shape, and shows the short stomodaeum (St) leading into the 

 coelenteron (C), which is partially subdivided by the radially placed 

 mesenteries (31). Each mesentery, whether complete or incomplete, 

 bears along its free edge a coiled mesenterial filament {MF). The 

 inner margin of the edge zone in such a section shows the cut ends 

 of a large circular endodermal muscle {Sp), which acts as a sphincter. 

 In his monograph on West Indian madreporarian polyps, Duerden 

 (: 02) states that this sphincter muscle is more strongly developed in 

 Isophyllia than in any other genus of corals studied by him. 



Owing to its large size the rose-coral polyp lends itself readily to a 

 study of its reactions to food materials. The colonies thrive well in 

 the laboratory, where they may be kept alive in running sea-water for 

 weeks. The best time for experimenting is at night, when the polyps 

 become fully expanded, and remain so in diffuse artificial hght. How- 

 ever, during the daytime all the feeding reactions may be obtained 

 from the partially contracted polyps, except those of the tentacles, the 

 latter then being withdrawn under the cover of the inner margin of 

 the edge zone. 



The Feeding Reactions. 



Movements of Oral Surface and Mesenteries. When a stream of sea- 

 water gently ejected from a pipette falls on the oral disk of a poljrp, 

 there is usually no perceptible response. If a drop of a concentrated 

 solution of Liebig's extract of meat in sea-water is similarly applied, 

 there is an immediate contraction of the retractor muscles of the mes- 

 enteries, which draws the oral disk downward. Simultaneously a vig- 

 orous contraction of the sphincter muscle takes place, and the edge 

 zone is drawn inward over the oral region, above which it forms a 

 temporary roof (Figure 2). Under the influence of a strong stimulus 

 the constantly diminishing central opening in this roof may finally be 

 obliterated by the meeting of the edges of the aperture, and the oral 

 disk below may thus become completely hidden from sight. 



Eversion of Stomodaeum and Extrusion of Mesenterial Filaments. 

 While this muscular reaction is taking place, and before the oral disk 

 is concealed, the stomodaeum may be observed to become everted, and 

 to project into the supra-discal space (Figure 2). The eversion of the 

 stomodaeum is accompanied by the extrusion of mesenterial filaments 

 through the mouth, together with the portions of the mesenteries to 

 which they are attached. Not only are mesenterial filaments thrust 

 through the oral aperture, but they are also extruded through the 

 discal wall itself (Figure 2). Duerden (: 02), who has observed this 

 behavior of the mesenterial filaments in many madreporarian polyps, 



