470 Common Objects for the Microscope. 
size of the spine; these spines have been termed the 
cathedral spines, from their resemblance to the spire of a 
cathedral; the comparison is not an inapt one. Each of 
the segments or vertebree of which the arm is composed 
supports about six of these spines; on each side, the 
largest are situated most laterally. There is a space free 
from spines along the centre both of the upper and under 
surface of the arm. Each spine presents a swollen base, 
and is attached by a regular articulation. 
Just within the lowest spine on the under surface of the 
arm is situate a very curious and beautiful body. It con- 
sists of a kind of claw, resting on an enlarged base, which 
is attached to the limb in a manner somewhat similar to 
the ordinary spines. The claw itself has two points, which 
are sharp and curved ; it is difficult to describe it in words, 
but it may be better compared to the head of a bird, with 
the beak widely open, than to anything else with which the 
writer is acquainted. These claws, when detached, appear 
to the naked eye no larger than specks of dust, but they 
may be well seen under an inch and a-half power; they 
look very transparent-and glassy ; they can readily be seen 
in their natural position by detaching a portion of the limb 
and holding it under the microscope by means of the stage 
forceps. 
The structure of the mouth, or as we should perhaps say 
more correctly the stomach, in this species is very remark- 
able. The aperture of the mouth is situated as in other 
star fishes in the centre of the body or disc, and leads 
directly into a cavity formed by five bones of very curious 
shape, which touch each other at their edges. Each bone 
presents a very perfect resemblance to the sole of a shoe, 
coming to a blunt point at the toe. The sole of each shoe 
is turned inwards, and the toe is directed towards the mouth 
of the animal. Each of these curious bones is perforated 
with a series of holes along each side, those at the heel 
part are largest, and occasionally the corresponding holes 
run into each other in the centre; passing on to the 
constriction of the bone, which corresponds to that of a 
shoe beneath the instep, the lateral holes become much 
smaller and diverge from each other till, towards the toe 
they are completely lost, but along this part of the inner 
surface of the bone there is a groove or depression. The 
holes as well as the central groove are for the attachment of 
a number of teeth; these teeth which are attached to the 
part we have called the heel of the shoe are of considerable 
