364 G. H. PARKER 
Renilla, moreover, as Lightbown (’18, p. 5) declares, is probably 
a specialized form, hence the detailed application of such a 
scheme to other forms should await experimental study. 
SUMMARY 
1. Renilla amethystina contracts and buries itself in the sand 
of its natural habitat as the tide recedes, and expands above the 
sand when the tide returns. In contraction its volume may be 
diminished 88 per cent by the discharge of sea-water. 
2. Sea-water enters Renilla through the lateral siphonozo- 
oids and possibly in very small amounts through the autozodéids, 
which certainly serve for the entrance of food. It does not 
enter through the axial siphonozodid or the terminal pore of the 
peduncle. 
3. Sea-water leaves the body of Renilla through the axial 
siphonozodid which normally discharges from time to time. 
Under high pressure water may also escape through the lateral 
siphonozodids, the autozodids or even the terminal pore of the 
peduncle. 
4, Within the body of Renilla the sea-water that enters by the 
lateral siphonozodids collects in the inferior canal of the rachis 
and passes thence either by very fine openings of the peduncular 
septum from the inferior canal to the superior one and thus 
less directly but more freely out at the axial siphonozodéid, or, 
5. The sea-water is drawn into the colony by the action, proba- 
bly ciliary, of the lateral siphonozodids and is expelled by general 
muscular contraction. 
