100 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 
under the names Virgularia elongata* and V. gracilis,t was observed by 
Dr. W. H. Dall in Catalina Harbor, Catalina Island, Cal., darting or 
swimming just below the surface of the water, and his observation 
LT regard as especially valuable and confirmatory as to the mobility of 
these animals. If they can move when compelled to do so, through being 
disturbed in an unusual manner, it is difticuit to perceive why they may 
not sometimes move of their own instinct or volition, using this last 
word in arestricted sense. The reasons from analogy are in my judg- 
ment full as weighty on the side of mobility as on the other, and the 
testimony of those who have actually seen these animals in their native 
element, including intelligent and ordinary observers, sustains the im- 
plication conveyed by the forms of the axial rods. The most active of 
the groups are quite likely sluggish animals, generally fixed and seden- 
tary; probably not able to continue actively in motion (motion en masse) 
for any great length of time. 
As to the mobility of one group as compared with another, it would 
seem as if those forms wherein the axis is simplest, the pinnz the most 
prominent, or the individual polyps the most numerous, might have an 
advantage over the others. As to the character of the motion, when 
the mass as a unit is detached and moving (swimming) which involves 
reciprocal and rather complex muscular action and implies a more elab- 
orate muscular system than these animals possess, hardly conveys the 
proper idea. Whether the motion requires primarily the simple satura- 
tion or absorption of water by and through the general mass, through 
pores in the basal section or through alleged or suspected terminal ori- 
fices of the interdermal longitudinal canals, or via oris—namely, through 
the mouth of each individual polyp—the propulsory movement is un- 
doubtedly due to a sudden act of the ceenosarec, a spasmodic and con- 
tractile effort by which the water is ejected and forced out via oris by 
the simultaneous co-operation of all the polyps in the mass. The move- 
ment would be better defined by the word “darting,” which is used 
by the fishermen who have seen it. 
Before closing, I should refer to what appears to be another important 
assisting factor in holding on to the bottom, in forms like Verrillia, and 
which is conspicuously exhibited in the species described by Mr. Fisher. 
I allude to the bulbous expansion which the ce@nosare in that species 
presents at a point just above the falciform termination of the style, 
and also to the elongated bulb of the basal end in Verrillia. Dr. Moss 
refers to this in his article heretofore quoted, and I am prepared to find 
it pertains to all of the simpler stalked forms. As will be perceived at 
a glance, the dilatation of this part materially assists in anchorage, and 
the contraction also readily admits of withdrawal. 
In relation to the geographical distribution of these interesting forms, 
I may add in this connection the discovery of another habitat for Ver- 
*Proc. Cal. Acad., Vol. II, p. 167. 
tId., Vol. III, p. 120. 
