LIVING SPECIES. 433 
the existing family of star-fishes, and approach 
most nearly to the Comatula ; (see Miller's Cri- 
noidea, PL 1, and p. 127): the bony skeleton 
constitutes by far the largest portion of these 
animals. In the living species this bony frame- 
work is invested with a gelatinous membrane, 
accompanied by a muscular system, regulating 
the movements of every bone. Although, in the 
fossil species, these softer parts have perished, 
yet an apparatus for muscular attachment exists 
on each individual bone.* 
The calcareous joints which compose the fingers 
of the P. Europaeus, together with their tentacula, 
are capable of contraction and expansion in 
every direction ; at one time spreading outwards, 
like the Petals of an open flower (PI. 52, Fig. 2), 
and at another rolled inwards over the mouth, 
like an unexpanded bud ; the office of these 
organs is to seize and convey to the mouth its 
destined food. Thus the habits of living animals 
illustrate the movements and manner of life 
of the numerous extinct fossil members of this 
great family, and afford an example of the va- 
lidity of the mode of argument, to which we are 
oblio:ed to have recourse in the consideration of 
extinct species of organic remains. In this pro- 
cess we argue backwards, and from the mecha- 
nical arrangements that pervade the solid portions 
* See the tubercles and corrugations on the surfaces of the 
bones engTaved at PL 52, Figs. 7, 9, 11, 13, 14, 15, 16, 17. 
GEOL. r r 
