348 
rorULAR SCIENCE REVIEW. 
and the swelling on the madreporic tube, replaces the fifth 
Polian vesicle. The whole is as unlike the drawings given in 
text books as is usual in cases where a diagram is reported 
to be a truthful representation of nature. Moreover the canal 
is closely invested by other structures, and when full and in 
action must have contained a very minute quantity of water. 
It is said to have an internal cellular layer which is ciliated, 
and one can envy the eyes which saw this very probable fact. 
Between this more or less circular canal and the circular 
attachment of the stomach, is a ring of nerve which rests on the 
jaw close to where there is a suture or join between the stout 
or inner part of the jaw and the narrower portion, to which is 
attached the jaw plate. As a matter of fact this nerve is 
external to the stomach attachment and slightly above it, and 
it is internal to and below the circular tube. What modifications 
age may make I do not know, but that is the position in the 
young.* The closeness of the water- and nervous systems is of 
importance, especially if the circular tubular canal acts as a 
blood circulator as well, which is excessively probable. In order 
to understand the course of the branches of the circular water 
canal, a few words must be said about the jaws, to which 
allusion has been so frequently made. As already noticed, 
their under surface is seen internally or orally to the side mouth 
shields, and two are placed together in each angle, their sides 
supporting the mouth papillse and their inner end the jaw plate 
and its tooth papillae and teeth (figs. 4, d ., 7, d ., 9, d.). The 
upper surface can be seen by removing the skin of the upper 
part of the disc and opening the stomach (figs. 5 and 9). The 
jaw plate and its teeth are seen to be attached to two 
rather diverging pieces, and these are the upper part of the 
pair of jaws of the angle, rather separated externally. Still 
further out, the separation increases, and an irregularly triangular 
piece is connected internally with the short diverging jaw, and 
is called the jaw or mouth frame. The mouth frame, one to 
each jaw, unites on one side with the mouth frame of the jaw 
of the next angle, and on the other, does not unite with that of 
its fellow jaw of the angle, but a space exists. The united 
mouth frames are in contact externally with the first plates of 
the arm, and the vacant space between the frames of the jaws 
which coalesce within, is in relation with the cavity of the body 
which is outside the stomach — the generative cavity. The arm, 
then, springs as it were from the union of the outer parts of the 
* Edward Forbes described the nerves of the Daisy Brittle Star, and 
noticed that there were no ganglionic enlargements, and he stated that each 
arm was supplied with two pairs of nerves from two sets of the main 
division . — British Star-fishes, c. viii. 41. 
