480 G. H. PARKER 



called attention to the striking contrast in the rate of action 

 between the longitudinal mesenteric muscles in Metridium and 

 such muscles as those of the sphincter or the foot in this form; 

 the rate at which the animal can withdraw the oral disc is in 

 the strongest contrast to that at which it covers the disc or 

 creeps about. Jordan is inclined to ascribe this difference to 

 the muscles themselves, but I have brought forward evidence 

 to show that these differences in rate are dependent in part at 

 least upon the presence or absence of nervous connections. The 

 acontial muscles are extremely slow in response and the forma- 

 tion of a constriction groove by the circular muscle of the col- 

 umn is a matter of minutes. The first of these is, I believe, 

 absolutely unassociated with nervous activity and the second 

 can take place after nervous activity has been temporarily 

 obliterated. It would therefore appear that these very sluggish 

 movements are dependent upon muscle unassociated with 

 nerve and that when these two elements are combined in a high 

 degree of differentiation, as in the longitudinal mesenteric sys- 

 tem, the rate of response becomes relatively high. 



Another matter of general importance in the nervous activity 

 of sea-anemones is the question of reflexes. It has been generally 

 believed that the neuromuscular system of such an animal as 

 Metridium could exhibit tonus and rhythmic motions, but noth- 

 ing comparable to the sharply marked individual reflexes of 

 the higher animals (Jordan, '08, p. 223), and this condition is in 

 general true. But there are, nevertheless, some responses in 

 Metridium that are strikingly like the individualized reflexes 

 of the higher forms. For instance when acidulated sea-water 

 is put upon the lips and the only response that follows is the 

 opening of the oesophagus by the contraction of the transverse 

 muscles of the complete mesenteries, a condition is presented 

 which, since it can be revived again and again, shows all the 

 characteristics of a highly individualized reflex. I am fully 

 aware that this instance and others like it imply in the nervous 

 structure of Metridium a definiteness of conduction tracts that 

 argues against a diffuse nervous system, but I believe these 

 cases to be exceptional and to represent merely the first signs 



