302 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, 

 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 would, in this case, have rendei'cd 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 f, 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 parlier page, 91, contrasting the Act'micB, wliich are locomotive, 

 with the PennatulidcB, which are, according to tlie better opinion, not so, 

 but which are permanently fixed in the soft mud, I suggested that the Ven- 

 triculida^ 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 

 V^entriculidae 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 the 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. 



