ACTIVITIES OF COLONIAL ANIMALS 507 
same diffuse way; they are both temporarily interrupted by the 
action of magnesium sulphate; they have essentially the same 
rate, and they are both quickened by high temperatures and 
slowed by low ones. Because of these points of resemblance I 
believe them to be one and the same thing, a diffuse nervous 
transmission carried out in all probability by an unpolarized 
nerve-net. This view is supported by the fact that the rate of 
this transmission, 7.39 to 7.83 cm. per second, is not far from 
that for the nerve-net of the sea-anemone Metridium, namely, 
between 12.1 and 14.6 cm. per second (Parker, 718). In both 
Metridium and Renilla, however, the rate is relatively low as 
compared with that found in jelly-fishes, namely, 22.9 cm. per 
second for Aurelia (Romanes, ’78) and 77.5 cm. per second for 
Cassiopeia (Harvey, 712). 
The transmission in Renilla that has just been discussed con- 
trols colonial contraction, the general withdrawal of autozodids, 
and, at night, phosphorescence. If these three activities depend 
for excitation upon one nerve-net, it might be supposed that, at 
least when phosphorescence is possible, all three should invar- 
iably occur together and that their independent appearance 
would be impossible. That they are more or less independent is 
quite certain. At night a slight stimulus may be followed by a 
momentary phosphorescence and with no other result. A 
stronger stimulus involves usually not only phosphorescence, but 
also the withdrawal of the autozodids and, if the stimulus is 
still stronger, general contraction may follow. It, therefore, 
appears that though these three activities may be controlled by 
a single nerve-net, they may exhibit a certain amount of inde- 
pendence, for apparently the intensity of the stimulus determines 
which particular activity or combination of activities may be 
called forth. Phosphorescence is excited by the slightest provo- 
cation; the withdrawal of the zodids requires a higher degree of 
activity, and general contraction is produced only by still more 
vigorous stimulation. 
The fact that at night I have never seen general contraction 
excited without zodid withdrawal and phosphorescence, and that 
the stimulus to zodid contraction is always productive of phos- 
