162 



Papers from the Department of Marine Biology. 



When further reduction in area was desired, linear strips of constant 

 width, each with a single sense-organ, were cut from the body of large 

 medusae, so that the area could be accurately reduced to -gW, VT> 

 T i and -=5-5-8- that of the original area. The fall in rate, as recorded 

 for the few observations made, when graphically represented produced 

 a continuation of the straight line obtained from the larger subdivisions 

 of the disks. 



The elimination of any portion from the excitable area could be 

 produced^ by immersing that portion in a 0.4 m MgCl 2 solution, as 

 shown in figure 18. When the anesthetizing solution was contained 



30 



20 



10 



I 



/3Z 



FIG. 17. Showing graphically the results obtained from the study 

 of 140 disks when the area of tissue was successively reduced 

 to yV the original area. The broken line extending to an 

 area ^4 the original is based on a smaller number of observa- 

 tions. The divisions along the ordinate represent the number 

 of pulsations; those along the abscissa represent the area of 

 tissue under the influence of the sense-organ. 



in the middle vessel the nerves were capable of transmitting the impulse 

 across this area, where the muscles were inactive, to the tissue in dish 

 No. 3, so that^the inactive area could be obtained at any point in the 

 strip of ^tissue. No differences in the results were obtained when the 

 activity, of a given area of muscles was eliminated by the cutting of 

 the subumbrella tissues or their immersion in the MgCl 2 solution. 

 Pieces of tissue in sea-water were found to be capable of responding to 

 each separate induction shock when applied at the rate of 126 per 

 minute when they had been reduced to ^{^ of the original area of the 

 strip which represented scarcely more than y-jj-trTnr (-oVr:^) f the area 

 of the original disk. 



This fact makes it apparent that the decline in rate of pulsation 

 caused by reducing the area enervated by a single sense-organ is not at 

 all dependent upon the necessity for a latent period on the part of the 

 muscular tissues. On the other hand, there is no apparent reason why 

 the sense-organs should be incapable of carrying on at the usual rate the 



