ASTEROIDEA 561 



them and the nerve ridge is the perihaemal vessel, divided by a septum 

 in which runs the '* blood vessel". The gonads are ten in number, 

 shaped like bunches of grapes and varying in size with the season. 

 They are attached to the body wall by their ducts, which open one 

 on each side at the base of each arm. 



st.c 



Fig. 418. Part of the aboral half of a starfish (Asterias rubens) removed, with 

 the alimentary canal, from the rest of the body, and viewed from within. One 

 lobe of the stomach has been cut away, and another partly turned back. The 

 detached figure represents an enlarged view of the axial sinus and adjoining 

 structures. From Borradaile. abo.m. aboral muscle; ax.o. axial organ; ax.s. 

 axial sinus; l.st. one of the lobes of the stomach; oes. oesophagus; pyx. 

 pyloric caecum; py.d. pyloric duct; py.s. pyloric sac; r.cm. rectal caecum; 

 sep. septum; stx. stone canal. 



Asterias (Figs. 408, 411, 415-418). A typical member of the class 

 Its principal features have been mentioned above. British. 



Astropecten. Without anus; without suckers on the tube feet; and 

 with conspicuous marginal ossicles. Lives on a bottom of hard sand, 

 into which it burrows, and upon which its tube feet are adapted to 

 walk. British. 



Bl 36 



