ACTIVITIES OF COLONIAL ANIMALS 347 
they are the chief inlets for Renilla, but Musgrave (09, p. 472) 
regards them both as inhalent and exhalent apertures. The 
third kind of opening is a well-defined pore, the axial siphonozo6id. 
This lies on the superior surface of the rachis near its center and 
at the end of a smooth tract of integument that starts from the 
root of the peduncle. This pore was first recorded by Miller 
(64, p. 354), who regarded it as the chief inlet and outlet for 
water in Renilla. Wilson (’83, p. 725), on the other hand, desig- 
nated it as the exhalent zodid for the colony. It probably cor- 
responds to the group of four pores in the axis of the dorsal 
face of the rachis of Pennatula mentioned by Musgrave (’09, 
p.454). Finally, there remains the problematic terminal pore sup- 
posed to be present at the distal end of the peduncle and regarded 
by various investigators as an inlet or an outlet aperture. These 
four classes of openings may now be considered in the order 
named. 
The autozodids 
The true polyps or autozodids of Renilla, as already stated, 
are disposed upon a somewhat irregular radial plan over the 
superior surface of the rachis of this animal. Near the center 
of the rachis they are relatively large and, when fully expanded, 
they may measure as much as 6 mm. in height. Toward the 
outer edge of the rachis they become smaller and more numerous. 
Each autozo6éid carries at its distal end eight pinnate tentacles 
surrounding an elongated slit-like mouth. One autozodid lies in 
the axis of the rachis and opposite the peduncle from the axial 
siphonozoéid. This autozodid, as has been shown by Wilson (’83) 
represents the original polyp produced from the egg, from which 
the remaining polyps of the colony have been formed by budding. 
The axis of the mouth of this autozodid agrees in direction with 
that of the colony as a whole. Those of the mouths of the 
other autozodids are in a similar manner in line with appro- 
priate lateral axes. Marshall (’83, p. 140) showed that in the 
lateral autozodids of the sea-pens the angle of the mouth that 
was turned away from the chief colonial axis, the abaxial 
angle, leads into a ciliated groove, the sulcus or siphonoglyph, 
