350 G. H. PARKER 
expands with its distal wounded end fully distended and closed 
as by a puckering string,—further evidence of the sphincter-like 
action of the distal half of the zodid. All these operations occur 
in such a way that it is clear that the fluid inside the colony is 
ordinarily under a slight continuous pressure. Nevertheless, 
both methylen blue and carmine gave under ordinary conditions 
not the least evidence of water currents emerging from the mouths 
of the autozodids or entering them, and I am forced to conclude 
that while the autozodids of Renilla are effective means of intro- 
ducing solid materials into the colony and of discharging like sub- 
stance from it, they play no important part in the exchange of 
sea-water whereby the colony as a whole expands or contracts. 
Under considerable and unusual pressure they may aid somewhat 
in the discharge of water, but even in this respect they are cer- 
tainly insignificant in their action as compared with other struc- 
tures to be considered presently. So far as sea-water ‘is con- 
cerned, they are, in my opinion, neither the chief inlets or outlets 
of the colony (Agassiz, 50, p. 209) nor even subordinate ones 
(Musgrave, ’09, p. 472). 
The lateral siphonozodids 
Seattered irregularly among the autozodids of Renilla are 
groups of small whitish bodies, the lateral siphonozodids, first 
clearly recognized by Verrill (64 b, p. 12). Each group consists 
of a variable number of pores, the lips of which exhibit, as a rule, 
eight lobes, thus indicating that each pore represents a single 
zooid. Not infrequently pores are met with whose size and struc- 
ture suggest that they may be aborted autozodids, but even in 
the extremes of these cases the whole body has a greater resem- 
blance to a siphonozoéid than to an autozodid, and since actual 
transitional forms between the two kinds have never been found, 
it is probable that in Renilla the two classes, the autozodids and 
the siphonozodéids, are entirely distinct. 
Each siphonozoéid pore is surrounded by a ring of whitish 
substance, in color and texture like that at the base of the auto- 
zooids, and the whole group of siphonozodéids is set in a field of 
