ACTIVITIES OF COLONIAL ANIMALS 495 
lobes by incisions that enter it symmetrically from its peduncular 
margin and it is stimulated at the root of the peduncle (fig. 10), 
a symmetrical wave of light spreads over the central lobe and 
into the lateral ones. If a lateral lobe is stimulated, the wave 
passes to the apical margin and thence onto the other two lobes. 
If the rachis is cut into a scroll that can be unfolded into an elon- 
gated form (fig. 11), stimulation at one end will start a luminous 
wave that will pass to the other end. 
If a colony is split longitudinally through its chief axis and 
the halves remain attached only through the distal part of the 
peduncle (as in fig. 3), the stimulation of one half-rachis calls 
forth a flash of light in that half which, after it has subsided, is 
followed by another flash in the other half. The second flash 
follows the first at such an appreciable interval of time that the 
preparation seems to wink first with one eye and then with the 
other. In such a test as that just described the interval between 
flashes is due to the transmission of the wave of excitation through 
the non-luminous peduncle, for if the peduncle is completely 
split no such transmission occurs even if the halves of the peduncle 
are closely applied to each other. This observation shows that 
the luminous waves are under the control of some form of trans- 
mission, non-luminous in character, that spreads in wave-like 
fashion and for which the phosphorescent waves may be said to 
be luminous replicas. It also makes clear that the peduncle 
can transmit the impulses that excite luminosity in the rachis. 
Not only can the peduncle transmit these impulses, but it can 
also originate them, for if the distal end of the peduncle of Renilla 
is pinched, in a moment the attached rachis flashes in waves of 
phosphorescence. Even when the peduncle is split longitudinally 
and the cut is carried through much of the rachis toward its 
apical margin, the stimulation of the distal end of a half-peduncle 
will call forth in the half rachis of the stimulated side waves of 
light that pass over quickly onto the half-rachis of the opposite 
side. 
As might be inferred, any portion of the rachis carrying the 
white material already alluded to can be made on stimulation 
to glow. Thus right or left halves, apical or peduncular seg- 
