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 (CASSIOPGA) 
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. The 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 
