158 



ARCHICCELOMA TA. 



really emerge from small holes between the ambulacra! 

 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 oj^al 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 



Fig. 91. — Median Longitudinal Section through the 

 Starfish in the plane of its Symmetry. 



Madreporite.^ 

 Stone Canal. 



Pericardium. - 



Cardiac part 

 of Stomach.' 



Axial Sinus. ' / 

 Ovoid Gland. 



Water Vascular Ring 



Ambulacral Ossicles. 

 Water Vascular Vessel. 

 Radial Nerve. 



ijii 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 retractor 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 coelom is spacious and is cut into during dissection. 



Vascular ^^ ^^ divided into several separate parts. The 



most important is (i) the water-vascular system 



(or ambulacral system). This is a part of the coelom in 



which is concentrated the motor function found elsewhere 



