NOTES ON THE OPHIURANS, OR THE SAND AND BRITTLE STARS. 347 
There is a plan which I have adopted in investigating the 
rough anatomy of the Ophiurae, which may be of use to other 
investigators, especially if they have time to follow out the 
structural details which are rendered manifest by it. Get a 
small specimen of Ophioglypha , and put it in weak hydrochloric 
acid and water, 1 in 100 at first, and then 1 in 20, washing often 
in clean pure water. Too much bubbling must not be allowed, 
for it destroys the tissues, but if the solution of the carbonate 
of lime proceeds steadily and slowly, a very remarkable prepa- 
ration may result. It is difficult to get rid of all the carbonate 
of lime, especially from within the arms, but sufficient may be 
dissolved to give capital views of the anatomy. 
One detail soon becomes evident on the under surface of the 
animal, and that is the lower limit of the stomach. Turn the 
preparation on its proper upper surface, and examine the lower 
by transmitted light, and a wide circle of tissue is seen hidden 
more or less, by the transparent tissue which was once jaws. 
It fills up the slits between the angles nearly to the level of the 
jaw plate, and there is no passage there into the side of the 
angle. On this lower surface of the stomach, or in the proper 
position of the animal under it, but close to its attachment 
to the jaws, is a canal or tubular membrane. It can be seen to 
give off branches, and to make its way as a microscopic tube 
into the arms, running in the median line on the under surface 
beneath the lower arm plates, which are of course all dissolved 
away, so far as their mineral part is concerned. It is a circular 
tube surrounding the insertion of the stomach into the jaws at 
a little distance and branching for every arm. In a little 
Ophioglypha , the body of which is less than ^ inch across, the 
tube is about — ^ inch in diameter after the acid treatment. 
The tube lias swellings on it called Polian vesicles. In the 
instance before me, a short membranous tube leads from , the 
perforated or madreporic mouth-shield to a globose enlarge- 
ment, whose diameter is five times that of the tube, and a cor- 
responding tube makes its exit on the other side and then 
slants off to the circular tube, which it joins. This is the feeder 
with water, from without ; and in its passage from the mouth- 
shield to the circular tube, it runs upwards and slightly inwards 
between the root of two arms and outside the stomach mem- 
brane, and between it and a membrane about to be considered, 
and which has to do with the reproductive organs. The swell- 
ings or Polian vesicles on the circular tube, usually said to be 
four in number, are simple enlargements of its muscular walls, 
with a slight increase of calibre on one side of the axis of the 
tube, and they are found close to the position of the off-giving 
of the radial vessels of the arms. In the specimen of Oph 'o - 
glypha , the tube is pentagonal and not circular in direction, 
