228 ZOOLOGY 
number of vessels. They constitute the blood system according 
to French authors. The radial one has already been mentioned ; 
the five radials unite with a circum-oesophageal ring, which is 
stated to open into the body-cavity by five interradial pores. 
Inside this is another ring-shaped vessel, into which a large 
sinus surrounding the stone canal—the axial sinus—opens. 
Besides this there is an aboral pentagon which sends off inter- 
radially pairs of vessels which dilate and surround the genital 
organs. 
The mouth is situated centrally on the ventral surface, 
surrounded by a ring of nervous matter. The mouth leads by 
a short oesophagus into a large stomach, the walls of which are 
folded in many saccul. When the starfish attempts to devour 
young molluses or shellfish which are too large to be taken in 
at the mouth, these sacculi are protruded and enclose the prey. 
They are retracted by special muscles. The walls of both the 
oesophagus and the stomach are ciliated, and the eversible 
portions contain many glands, the secretions of which possibly 
exercise a paralysing effect on the prey. The stomach is 
followed by a pentagonal pyloric portion with its angles 
situated radially. From each angle a short duct passes to 
the base of each arm, and here opens into two large hepatic 
caeca, which occupy a large portion of the space in each arm 
and extend to its tip. Each caecum is supported by two dorsal 
mesenteries. From the pyloric portion a short rectum passes 
to the anus, which is in the next interradius to that bearing 
the madreporic plate, and is almost central. The rectum gives 
off two short caeca, which lie in two neighbouring interradii 
—that between the left and central arm of the trivium, and 
between the left arm of the trivium and bivium. 
The water-vascular system consists of a circumoral ring 
which gives off five radial vessels, one running along each arm, 
and a single interradial stone canal, which passes from the 
circumoral ring, and opens to the exterior at the madreporic 
plate, which is calcified. 
The madreporic plate is marked externally by a number 
of radial grooves; at the bottom of each of these is situated a 
row of pores; these open into a series of tubules, which collect 
into an ampulla, and this in its turn opens into the lumen of the 
