198 J. D. Dana on Zoophytes. 
of the little animal are here folded away (fig. 5.)* Thestomach 
communicates with the tubular cavity below it, (figs. 4, 5,) and 
empties into this cavity the chyloid fluids after digestion. There 
is thus a community of visceral cavities often throughout a whole 
group, and the several polyps eat for the general good. ‘The flu- 
ids (as the writer has observed, but which has been more’ fully 
ascertained by Lister and others) vibrate back and forth, or have 
a cyclosis movement like the circulation in a Chara, sometimes 
flowing quite into the stomach again; in connection’ with admit- 
ted water, they take the place of a proper circulating fluid.f 
There are floating particles as in the circulating fluid of other 
animals. Thus aération and assimilation go on without any of 
the usual appurtenances of gills or glands. 
The tentacles are commonly slender tubular,t and become ex- 
panded by injection with water. They usually aid in capturing 
animalcules, minute crustacea, or whatever prey comes within 
reach; and they apply themselves to the work, with considerable 
dexterity, though less nimble than the more active Bryozoa. In 
some species, they are short and sluggish, sa can subserve out 
the purpose of aération. 
i iotu. te 
* There a 2 oes here to be a'retreat into a cell; but in fact, it is only the head 
or upper part of the polyp, and not the polyp itself, which becomes concealed. 
‘The whole animal has a c artilaginous or corneous exterior, exce 
summit and tentacles, and these c consequently, on contacting, fal fall down into the 
extremity of the tube. This extremity is the part about the stomach, and the an- 
imal is usually pes here than below; when not ated there is generally me _ ré- 
traction of the polyp : 
+3... ae Philosophical Trausactions, 1834, p- 369, rite fine ‘illustrations on 
‘idieas 9 and 1 
We quote ee following from his very interesting observations. The geri 
‘* flowed in one channel, alternately backwards and forwards, through Speci 
the particles were hardly distinguishable; but it became much slower when neat 
the change. Sometimes it returned almost without a pause; but at other times it 
was quiet for a while, or the particles took a confused - ‘whirling motion for a few 
Seconds; the current afierwards ‘appearing to. set the stronger for the suspension.” 
ead lis and five flows occupied fifteen minutes and a half; the same average 
ing spent in the ebb as in the flow.’ Lister states that the vibrating mo-_ 
rae of the internal axial fluids were first noticed by Cavolini in his oe gence _ 
_ Servire Storia 
ia de’ Polipi Marini, published at Naples, in 1785. * 
The Tebslaride sod alos Ie 4 ‘a cir 
a en Hydra in not ing oo organs properly t mar e 
: ‘ihe eee oo stead of bred bavi = 334 with mi 
Sr — em) 
