ACTIVITIES OF COLONIAL ANIMALS 481 
once in 130 seconds and pass over the colony in approximately 
115 seconds and that the average resting period is about 15 sec- 
onds. As may be inferred from what has been stated, never 
more than one rachidial wave at a time is to be seen on a colony. 
In specimen A of those referred to in the preceding paragraph 
the distance traversed by the waves over the peduncle and rachis 
measured 148 mm., and as this course was covered on the average 
in 130.2 seconds, it follows that the rate at which the wave trav- 
eled was 1.1 mm. per second. In specimens B and C the respec- 
tive courses measured 117 and 133 mm., and the rates in these 
colonies were, therefore, 1.1 mm. per second for B and 1.3 mm. 
per second for C, or an average of approximately 1.2 mm. per 
second for all three. This rate is of the same order of magnitude 
as that already found for peduncular peristalsis, namely, 1.2 
mm. per second. The similarity in rate in these two forms of 
peristalsis indicates that the organization that underlies them 
’ must be essentially the same, though reversed so far as polarity 
is concerned. 
The rate of 1.2 mm. per second for rachidial peristalsis was 
determined in sea-water at 23°C. Efforts were made to ascertain 
whether this rate was influenced by changes of temperature, but 
at 15°C., the irregularities in the responses of the colonies were 
such that measurements were not possible, and at temperatures 
much above normal no rachidial peristalsis occurred. 
The rachidial peristaltic wave ordinarily makes its first appear- 
ance in the distal half of the peduncle and spreads thence as a 
right and a left wave symmetrically over the rachis, at whose 
apical margin the two waves meet and obliterate each other. 
If an incision is made on one side of the rachis (fig. 1), the wave 
passes around this without suffering interruption, even though 
the cut may reach well toward the center of the colony. Sev- 
eral cuts of this kind may be made in one or both sides of the 
rachis without interrupting the wave. If a single lateral cut is 
made from one side of a rachis through its center well toward 
the other side (fig. 2), the wave that would naturally pass up 
the incised side is interrupted at the cut, whereas that which 
traverses the intact side not only reaches the apical margin, 
