362 Mr. Toulmin Smith on the Classification 
sea-water, just as in any single specimen of Ventriculites or 
Cephalites. 
But the contrivances in this species to secure the well-being 
of the myriads of its tenants, and so strikingly indicative of de- 
sign and adaptation, do not end here. Thin and delicate as the 
wall is, though greatly strengthened by the fact of the upper as 
well as the lateral margins of each lobe being closed, the cur- 
rents, small as they would be, caused by the streams continually 
pouring out of these lateral perforations, or lungs as they may well 
be called, might tend to displace the form ; — a matter of pecu- 
liar danger in species having such extended surfaces in such 
close apposition, their distance seldom exceeding one line. 
Besides this, such broad flat surfaces as the lobes or arms here 
take would offer so much resistance to the slightest impulse that 
the walls would be more liable than those of other species to 
suffer displacement ; while there is no membrane, as in Cephalites j 
stretching across and attached to each to secure them in posi- 
tion ; a contrivance indeed which, though so admirably adapted 
to all cases in which it is found, the length and depth and entire 
distinctness of the arms w^ould, in this case, have rendered but 
very imperfectly effectual. 
To secure the animal against such dangers I have further found 
that, while the central root* is comparatively small, merely acting 
as an anchor, there depended a single root-fibril from between each 
of these perforations to a considerable height on all sides of the 
entire animal. By these then was it maintained securely in shape 
and in position. These depending fibrils acted exactly like the 
* In an earlier page, 91, contrasting the Actinice, which are locomotive, 
with the PennatulidcB, which are, according to the better opinion, not so, 
but which are permanently fixed in the soft mud, I suggested that the Ven- 
triculidm might possibly combine both these qualities, and have a locomotive 
power, fixing themselves firmly, during pleasure, in the soft mud. However 
difficult it may be to arrive at certainty on such a point, the inquirer will pro- 
bably be inclined to acquiesce in the doubtfulness with which this sugges- 
tion was offered, after considering the very peculiar arrangement of roots in 
the present species. The roots of this family of compound animals fulfilled 
the same purpose as the peduncle of the Terebratula. They differ indeed in 
structure from the latter, — for the opportunity of examining which, in the 
recent state, I am again indebted to the kindness of Prof. Owen, — but, in 
this respect, the hyssus of the Pinna, with an analogous function, differs yet 
again from both. But it is a curious and important fact that the roots of 
Ventriculidae are never found attached to rock or shells, though shells are 
often attached to parts of the surface of the body and roots : nor have the 
minutest shells ever penetrated the substance of tlie body, as they continu- 
ally do in sponges. 
f How high it is almost impossible to ascertain. It has been with the 
greatest difficulty that I have ascertained the fact at all, as it is only by fol- 
lowing the small fibril with the knife that its presence can be detected or its 
direction traced. 
