242 Papers from the Department of Marine Biology. 



Since the respiration is influenced by the muscular activity or pulsa- 

 tion-rate, and the latter is not constant, it was decided to remove the 

 ganglia (rhopalia) that induce the pulsations and start a continuous 

 contraction-wave running around the subumbrella (the middle third of 

 which has no neuro-muscular tissue, Mayer, 1908). The rhopalia 

 were cut out by means of a cork-borer and the wave started by electrical 

 stimulation. It was noticed, however, that the contraction-wave, 

 apparently constant for short intervals of time, changed more rapidly 

 at first and then more slowly, but never became absolutely constant, 

 the change being perhaps associated with shrinkage of the umbrella. 

 The effect of shortening and stretching on the contraction-wa^e was 

 therefore studied. The rate of the contraction- wave depends on the 

 rate of the nerve-impulse around the circuit of the nerve-muscle layer, 

 but does not depend solely on the rate in the neuraxon, since there are 

 numerous synapses, and furthermore, the path of the impulse is zigzag. 

 Prof. L. R. Gary kindly showed me a stained preparation of the nervous 

 network of the subumbrella. Concentric rings cut from the umbrella 

 are capable of maintaining a trapped wave for some time, but if the 

 ring is too narrow, the wave can not be started or soon ceases after being 

 started. Trapped waves can be started in 2 or 3 concentric rings cut 

 from the umbrella and the wave revolves about the inner ring more 

 often per second than about the outer ring, but the revolutions per 

 second are not in exact inverse proportion to the mean diameters of 

 the rings or to the diameters of the inside tracks or holes in the rings. 

 One subumbrella, 11.5 cm. in diameter, was cut into two rings and waves 

 were trapped in them. The wave in the inner ring made 2.5 revolu- 

 tions per second and the wave in the outer ring made 2 revolutions 

 per second. 



The uncertainty as to the length of the pace-making circuit that the 

 nerve-impulse takes around the ring may be avoided by stretching the 

 inner edge of the ring until it is of the same diameter as the outer, 

 thus transforming the ring into a cyUnder or belt. Such a ring can 

 be stretched further and behaves in a strikingly reversible manner. 

 Since Mayer (1917) has shown that the rate of nerve-conduction in 

 Cassiopea depends on temperature and electric conductivity of the sea- 

 water, it should be noted that all the experiments in this paper, unless 

 otherwise stated, were m.ade in sea-water of 30° and CI = 20. Mayer 

 found a variation of only about 2.5 per cent over the range of pH = 

 5.6 to 8.26, and this variation includes experimental errors and changes 

 due to unknown causes. In the present experiments the pH was about 

 8.2 unless other-^dse stated. The only difficulty in estimating the rate 

 of the contraction-wave arose from the fact that the rate is 1 to 5 per 

 cent faster in the ring that has just been stretched than in the ring that 

 has just been relaxed, depending on the degree of recent stretching or 

 relaxation. If, however, the circumference of the ring is allowed to 



