ACTIVITIES OF COLONIAL ANIMALS 363 
unaltered. Even the forceful opening of its axial pore, which 
during such an operation remains closed, will not allow the animal 
to discharge. This, however, can be accomplished immediately 
if the inferior canal in the rachis proximal to the ligature is cut 
open, or if the ligature is taken off, in which case, the axial pore 
immediately opens and the discharge takes place through this 
aperture. If the inflated animal as originally ligated be allowed 
to remain so, one of two things may happen. Usually it will 
very slowly contract till its volume has become extremely small 
or it will remain inflated and tense for along time. Clearly, these 
two conditions indicate different degrees of freedom of connec- 
tion between the superior and inferior: canals in the rachides of 
different individuals. In some, and these must be few in num- 
ber, there seems to be no connection between these two canals 
in the region of the rachis; in others these connections unques- 
tionably exist, though at best they are far from being as free as 
those invariably present in the peduncle. One may therefore 
conclude that in a resting Renilla water passes from the lateral 
siphonozodids to the interior system, whence it proceeds in small 
amounts slowly through the pores in the region of the rachis to 
the superior canal and in large amounts through the pores of the 
pedunclar septum to the same canal and thus out from time to 
time through the pore of the axial siphonozoéid. Under such 
normal conditions, it is probable that none of the other apertures 
of Renilla, the mouths of the autozodids and the terminal pedun- 
cular pore, are concerned in any significant way with the water 
current. 
When such a resting animal is stimulated so that its general 
musculature contracts and its fluid contents are put under unusual 
pressure, water may then escape from it not only through the 
pore of the axial siphonozodid, but through those of the lateral 
system and through the mouths of the autozodéids or even through 
the terminal pore of the peduncle. 
The scheme of water circulation that has been worked out for 
Renilla may perfectly well apply to other sea-pens. In many of 
these instances, however, as Musgrave (’09) has shown, their 
organization is much more complicated than is that of Renilla. 
