ACTIVITIES OF COLONIAL ANIMALS 483 
where it would ordinarily stop, but passes beyond this and down 
the opposite side to end at the cut. Thus for the latter extent 
of its course, after it has passed the apical region, it progresses 
over a part of the rachis in a direction the reverse of that which 
is normal for this part. Ifa Renilla is split in its axis from the 
apical region through its whole extent and the cut is carried well 
through the length of the peduncle, but not to its distal end (fig. 3), 
a single wave starts in the peduncle, but is soon represented by 
a pair of independent but synchronous waves that pass over 
the two halves of the rachis. If an axial cut is made in the direc- 
tion severing the two halves of the peduncle completely but 
leaving the halves of the rachis attached at the apical margin 
(fig. 4), two entirely independent waves arise, one from each half- 
peduncle. These waves differ from those in the preceding prep- 
aration in that they are not necessarily synchronous. ‘The single 
peduncular center from which in a normal colony the rachidial 
wave arises is in this preparation divided into two, and the two 
half-centers show complete and independent action. 
The cutting of incisions not only fails to prevent the formation 
of a rachidial wave, but considerable parts of a colony may be 
removed without loss in this repect.. Thus, although the rachi- 
dial wave ordinarily begins in the peduncle, this whole structure 
may be ablated without checking the formation of the wave. In 
a Renilla from which the peduncle has been cut the rachidial 
wave begins in what was the root of the peduncle and proceeds 
thence as a pair of waves along either side of the rachis to meet 
and disappear in a normal way on the apical margin. If instead 
of cutting off merely the peduncle, the whole center of the rachis 
is removed, the waves still start synchronously in the adjacent 
lobes thus produced and progress to the usual termination. If, 
now, one of the lobes is cut off (fig. 5), the wave as a single wave 
starts from the remaining lobe and proceeds not only to the api- 
cal margin, where it would ordinarily cease, but continues on- 
ward around the remainder of the edge of the rachis to the region 
where the lobe was cut off and ends there. If a preparation is 
made by cutting off a narrow band around the whole edge of the 
rachis, this band as well as the remaining central portion will 
