Papers from the Department of Marine Biology. 



cutting out the central stomach, and in addition a circular scratch 

 cutting through the nervous and muscular layer of the subumbrella, 

 thus separating the broad annulus of tissue into two rings. This 

 subumbrella tissue becomes paralyzed through the removal of the 

 marginal sense-organs, but the outer of the two annuli may then be 

 stimulated by an induction shock until a contraction-wave going in one 

 direction is entrapped in it, as illustrated in figure 4, and as has been 

 described by Mayer, 1906, 1908.* Such a 

 neurogenic contraction wave must travel con- 

 tinuously through the circuit of tissue which 

 has entrapped it, and may maintain itself for 

 days with but little change of rate, provided 

 the temperature, C0 2 , salinity, and hydrogen- 

 ion concentration of the sea-water remain con- 

 stant. Thus we have a means of entrapping 

 a single neurogenic stimulus which remains 

 practically uniform in intensity and rate for FIG. 4. Diagram showing a 

 any desired length of time. s ! n s le neurogenic pulsa- 



. . , . . , ,. ., , tion- wave coursing in one 



Strong stimuli travel faster than weak ones, direction through an an- 



nulus 

 tissue. 



of subumbrella 



and thus if a wave stops it can not be started 



again at the same rate, for no two stimuli are 



received alike by the tissue. Such circuit waves may be stopped by 



counter-waves proceeding in the opposite direction against them, or 



blocked in the nerve net without apparent cause (fig. 5); or, if the 



tissue be exhausted, as in the absence of calcium, or by heat, cold, or 



CO 2 , the wave may become irregular (fig. 13, lowest line) indicating that 



*f t tt * t it i it it i n ii 1 1 1 1 it n 1 1 1 1 i i 1 1 1 it 1 1 i i it 1 1 1 1 



1 1 1 1 ft 1 1 t t t t t 1 U 1 t t * t ! t 1 II I t t t I 1 t 1 1 1 U H 1 ) 



\, A - ;- .; ^i -A- >J 



FIG. 5. Two examples of sudden stopping of entrapped waves. Usually 

 the wave becomes somewhat irregular before ceasing. 



it is about to cease. In exhausted or weakened tissue, pulsus alter- 

 nans may be displayed by the wave, the muscles becoming capable of 

 responding fully only to every alternate (or even every second or third) 

 return of the nerve stimulus (fig. 6, lowest line) ; but in normal, healthy 

 tissues the wave is a full, regular sinusoid, the intervals being almost 

 machine-like in their rhythmic sequence. 



When a passive, paralyzed ring is activated by an induction shock, 

 as in figure 7, muscular tonus is at once developed, and irregular and 



Tarnegie Inst. Wash. Pub. No. 102, p. 116. 



