ACTIVITIES OF COLONIAL ANIMALS 355 
Only when the peduncle is pinched between the fingers does a 
fine jet of water issue from its tip. Hence it is necessary to 
consider whether this aperture is due to artificial rupture or is 
a natural one and, if it is such, whether it is an exhalent or 
inhalent aperture. 
To determine whether or not a natural pore exists at the tip 
of the peduncle of Renilla, the following tests were made. In 
ten fresh, vigorous animals the peduncle was pinched between 
the fingers till a jet of water appeared and the exact point of issu- 
ance was then noted. In six instances the jet issued with great 
regularity at the very tip of the peduncle. In two of the ten 
specimens two jets appeared one at the tip and the other on 
the side of the peduncle, but near the tip. In the remaining two 
the jets were from the side. In all instances the lateral jets were 
less regular than the terminal ones, as though the lateral jets 
issued through small ruptures and the terminal ones through a 
natural pore. 
Peduncles from ten fresh animals were then cut off and put in 
sea-water to which was added some magnesium sulphate. After 
three hours these peduncles were attached at their cut ends one 
by one to the tip of a vertical glass tube which was made to dip 
under the surface of a bowl full of sea-water. Sea-water colored 
with methylen blue was then run into the tube till it issued 
through the peduncle. In six instances it emerged through the 
exact tip of the peduncle in a very thin well-defined stream and 
when the column of colored water in the tube showed a height 
of from 12 to 15cm. In the four remaining peduncles it emerged 
as an irregular stream in each case from the side of the given 
peduncle. 
Normal peduncles, unanesthetized with magnesium sulphate, 
were then tried in the same way. In the most resistant of 
these the colored water flowed from the tip of the peduncle when 
the fluid in the tube reached the height of 115 em. and continued 
to flow till it fell to 40 em., when the opening closed. In the 
least resistant the flow began at 80 cm. of water pressure and 
was checked at 20cm. These observations, like those based on 
the position of emergence of the jets, favor the view that in 
Renilla there is a natural terminal pore on the peduncle. 
