E. W. BERGER ON THE CUBOMEDUS^. 19 



bottom instead of at the surface as at Port Henderson. It is possible 

 that the animals had been active near the surface earlier in the 

 morning and that some unknown conditions determined their settling 

 to the bottom earlier in the former place than in the latter. 



Conant's conjecture, " whether these were their natural conditions, 

 or whether the two forms," Charybdea and Tripedalia, "were driven 

 by some chance from the deep ocean into the harbor and there 

 found their surroundings secondarily congenial, so to speak," 

 seems to be borne out in favor of the former supposition (for 

 Charybdea at least), that these are their natural conditions and that 

 Charybdea Xaymacana is essentially a shore form. 



AURELIA AND POLYCLONIA (CASSIOPCEA) 



Experiments 42-53. 



Many of the observations on these forms relate to the rate of 

 pulsation. In an Aurelia, following the removal of a lithocyst, there 

 was a pause followed by pulsations. In about two minutes rhythmic 

 pulsations were renewed. Four minutes after the operation there 

 were nineteen pulsations to the half minute, while twenty minutes 

 after there were only nine, and these in groups of six and three. 

 The normal rate of pulsation was twenty-five to the half minute. 



Polyclonia behaved much in the same manner as Aurelia. Upon 

 the removal of lithocyst pulsations continued, but in groups with 

 short pauses. The normal rate of pulsation was twenty-seven to the 

 half minute, while three minutes after the operation it was 

 seventeen, and eleven minutes after, fifteen to the half minute. 

 The tissue connected with a removed lithocyst gave contractions. 

 Placing a Polyclonia in fresh sea-water more than doubled the 

 rate of pulsation, which, however, soon fell to the normal rate, and 

 lower in one instance. In small individuals the rhythm is decidedly 

 more rapid than in those of larger size. T.he few observations on 

 this point would seem to show that it is in inverse proportion to the 

 squares of the diameters of the bells. 



The removal of a single oral arm or of the whole eight, in 

 Polyclonia, had much the same effect as the removal of a lithocyst: 

 there was a decided slowing of the rate of pulsation, while the 

 immediate effect of cutting was an acceleration or a return to near 

 the normal rate. About a day later this same animal had quite 



