158 PROCEEDINGS OF THE AMERICAN ACADEMY. 



that previous to their discovery of differentiated ectodermal nervous 

 tissue in Coenopsammia no ectodermal columnar nerve or muscle layer 

 had been found in any madreporarian polyp. 



In spite of the apparent absence of adjuster tissues in the body wall 

 of Isophyllia, a transmission of at least a nervoid character takes place 

 from receptor to effector through intervening portions of the body. 

 The evidence for this rests on the results of experiments with both 

 chemical and tactile stimuli. 



As has been stated in the preceding pages, the application of meat 

 extract to the surface ectoderm is followed by an immediate contraction 

 of the sphincter and mesenterial muscles, both of which are, according 

 to Duerden ( : 02), situated in the endoderm. An impulse of some kind 

 must, therefore, pass through the intervening mesogloea, which in 

 Isophyllia is a layer of considerable thickness. 



A longer distance must be traversed by the nervoid impulse when 

 the retractor muscles of the mesenteries respond to a chemical stimulus 

 affecting the distal end of a tentacle. This reaction, following the ap- 

 plication of a bit of filter paper dipped in meat juice, has already been 

 described. 



There is evidence, furthermore, that the transmission of impulses 

 is not confined to the polyp stimulated, but may extend throughout 

 the colony. When meat extract is applied to a single polyp a wide- 

 spread effect is produced. For example, in one experiment a small 

 amount of concentrated meat extract was placed during the daytime 

 on the central ^olyp of a colony with twenty-five oral apertures. The 

 stimulating material soon spread over two adjacent polyps, which, with 

 the central one, became tightly contracted. Meanwhile stomodaea be- 

 gan to be everted and mesenterial filaments extruded all over the 

 colony, which in consequence presented, after two or three minutes, a 

 very ragged appearance. The sphincter and retractor muscles of these 

 outlying polyps were not appreciably affected. 



It must be admitted that the explanation of this reaction as due to 

 nervoid impulses from the central polyps is open to the objection that 

 the stimulus may have been local, owing to the difTusion of the meat 

 juice externally over the surface of the colony, or internally through 

 the communicating coelentera. This objection cannot be raised, how- 

 ever, in the case of a colonial reaction induced by a tactile stimulus 

 ai)plied to a single polyp. Especially at night, when the corals are 

 most sensitive, the touching of a centrally situated pol)q) with a piece 

 of wood or a glass rod will often be followed not only by an immediate 

 local muscular response, but also by a sudden contraction of the mesen- 

 terial muscles throughout the colony. The result is seen in the general 

 sinking of the oral surfaces. 



