508 G. H. PARKER 
phorescence, but not necessarily of general contraction, supports 
this view. It is, therefore, quite possible that all three activi- 
ties are controlled by a single nerve-net and yet possess a certain 
kind of independence, for apparently the strength of the stimu- 
lus may determine which particular activity or group of activi- 
ties may be made to appear. 
CONCLUSIONS 
The activities of Renilla, as given in this and the preceding 
paper, show very clearly the main outlines of the organization 
of this animal. Although its development, as worked out by 
Wilson(’83), gives indisputable evidence of the origin of the 
colony from a single zodid and shows that the zoéid is the mor- 
phological unit in its composition, its reactions center around 
‘the colony as a whole rather than around such units. In this 
sense the activities of Renilla make plausible the belief of many 
of the older naturalists that this and other sea-pens are individual 
-animals—a view which from the standpoint of morphology has 
long since been abandoned. 
The Renilla colony fills itself with sea-water through the lat- 
eral siphonozoéids and empties itself through the axial siphono- 
zooid, processes in which the ordinary polyps, the autozodids, 
appear to play almost no part. The movement of the water 
within the colony is chiefly dependent upon the general muscu- 
lature and particularly upon the two forms of peristalsis shown 
by this musculature, peduncular and rachidial. As these peri- 
staltic movements, by which the water within the colony is 
moved, are strictly colonial and as the water enters the colony 
and emerges from it through particular classes of zodids, the 
expansion and contraction of Renilla is a mixed operation, in 
part zodidal and in part colonial. 
Peduncular peristalsis has for its chief functions the anchor- 
ing and burying of the colony and locomotion. ‘These activities 
are general in character and essentially colonial, not zodidal. 
Rachidial peristalsis is the reverse of peduncular peristalsis in 
that it serves to elevate and expand the colony, but it is like 
peduncular peristalsis in that it, too, is strictly colonial. In both 
