INTKODUCTION, 
XIX 
merely tlie mechanical result of the impact of the ciliary 
current on the closed tip. If so, the current runs upward 
on the whole inner surface of the walls, and then returns 
down the centre. And this, I am persuaded, is the case. 
That the tentacles are perforated at the tip is, however, 
certain ; but it is closed or opened at the will of the animal, 
the outer annular layer of fibres acting as a sphincter. 
Nothing is more common than to see a fully expanded indi- 
vidual of T. crassiconits, when suddenly alarmed, eject 
slender streams of water from the tips of its tentacles ; and 
I have seen an instance in which, the animal being but just 
covered with water, the jets were projected to a height of 
three inches above the surface. In S. bellis, after macera- 
tion, the slightest pressure on these organs causes the 
pigment to ooze out at the tip. In many that I so treated, 
not one allowed it to escape at the side ; nor in any case 
was there the least appearance of resistance, suddenly 
yielding as if by a rupture ; nor did the aperture in any 
case enlarge, nor was it in any case otherwise than at the 
precise extremity. From which circumstances I infer a 
natural foramen there ; and think that it exists in all 
species, except those (as Corynactis and Cavyophyllia) 
which have a globose appendage at the extremity of the 
tentacle. 
The circulation of the nutrient fluid is aided by a curious 
apparatus of foramina, of which I have met with no 
description. It is difficult to find them in dissection, for 
they appear to close with contraction ; but in bellis, on 
making a transverse section just below the disk, I have 
found a small round aperture in each primary and secon- 
dary septum, through which I could thrust a probe without 
laceration. It is during life, however, that, under certain 
favourable circumstances (for they cannot at all times be 
detected), they must be studied. In diayitkus, when very 
much distended, I have seen the principal septa perforated 
with a large circular foramen in the midst of their broadest 
part, resembling iron girders supporting a floor, excavated 
for lightness (Plate XI. fig. 1, b). In Anthea cereus they 
are conspicuous;* but I have been unable to detect them 
in T. crassicornis or in Corynactis. 
* The most satisfactory observations I have made on these perforations 
were on a specimen of Anthea cereus, var. sulphurea. Being very much 
expanded, and distended to translucency, the base adherent to the side of 
a glass tank, the column greatly exceeding the base, the window opposite, 
b 2 
