158 ARCHIC@LOMATA. 
really emerge from small holes between the ambulacral 
ossicles arranged in a row on each side. These ossicles 
form the walls of the grooves. At the edges of the grooves 
are rows of calcareous spines, and a few extra large ones, 
the oral spines, project inter-radially or towards the mouth. 
At the tip of each arm is a small eye-spot. 
If the upper surface be entirely removed the alimentary 
organs are brought into view. The mouth leads into a 
spacious cardiac part of the stomach which is 
radially lobed. A constriction leads into the 
pyloric portion which is pentagonal in shape, the angles pro- 
jecting radially. From each angle there runs a duct which 
Alimentary. 
Fig. 91.—MEDIAN LONGITUDINAL SECTION THROUGH THE 
STARFISH IN THE PLANE OF ITS SYMMETRY. 
Madreporite.. 
Stone Canal. ‘bs 
} e Pedicellaria. 
Cardiac part 
of Stomach.’ 
ak oe 
os * Ambulacral Ossicles. 
*. Water Vascular Vessel. 
Axial Sinus.“ 7 Radial Nerve. 
, yy y 
Ovoid Gland. Water Vascular Ring. 
(If exactly median the section would cut the median mesentery and not the gonad.) 
bifurcates into two long pyloric glands in each arm. The 
intestine is very short and has a pair of small branched 
anal glands. It will easily be seen that the pyloric glands 
are attached to the aboral wall by paired mesenteries, 
and that the cardiac part of the stomach is attached 
to the oral wall by ze¢vactor muscles. The cardiac portion is 
often protruded (e.g., into oyster-shells) and prey is obtained 
in this way. The pyloric glands are said to be digestive 
in function and the anal glands mainly excretory. 
.The ccelom is spacious and is cut into during dissection. 
It is divided into several separate parts. The 
most important is (1) the water-vascular system 
(or ambulacral system). This is a part of the ccelom in 
which is concentrated the motor function found elsewhere 
Vascular. 
