452 G. H. PARKER AND E. G. TITUS 



Taf. 21, fig. 11). Structurally the acontium would seem to 

 be an ideal organ in which to test the transmission of nervous 

 impulses and the like, through its primitive nervous strands. 

 Pieces of acontia four or five centimeters long can be easily 

 obtained from a large Metridium and will continue alive and 

 active in seawater for many hours. When such a filament is 

 mechanically stimulated by agitating it in seawater or by drop- 

 ping seawater on it, or when it is flooded with dilute meat juice, 

 it twists itself into an irregular coil. This response takes place 

 slowly and only after a minute or two. If the stimulus is limited 

 to one end of a long acontium that end and that end only re- 

 sponds by becoming snarled. This reaction will occur as well 

 at the central end as at the peripheral end of a given acontium. 

 When acontia have been kept for twenty minutes or so in sea- 

 water containing chlorotone, a period long enough to anesthetize 

 the tentacles of an intact Metridium, they will still become snarled 

 when flooded with dilute meat juice exactly as unanesthetized 

 acontia do. When acontia still attached to a Metridium but 

 extending several centimeters away from it are variously stimu- 

 lated at their free ends, not the least response has ever been 

 observed in the Metridium itself though the acontia react vigor- 

 ously in the region to which the stimulus is applied. The stimu- 

 lation of their free ends seems to have no more influence -on the 

 Metridium than the cutting of the free end of a long hair has 

 on a human being. From these observations we conclude that 

 the acontia in Metridium have no nervous significance whatever 

 and that their muscles, are stimulated directly and in no other 

 way. What the so-called nervous tissue of the acontium really 

 is we cannot say. Possibly, as one of us has already suggested 

 (Parker, '12, p. 461), it may be a sj^stem of more open spaces 

 next the muscle cells and so arranged as to facilitate their nour- 

 ishment and the removal of their waste. Of' this, however, 

 we have no proof. What we wish to emphasise is the com- 

 pletely non-nervous nature of the acontium. 



