OPHIURA. ' 75 



3. The thickened, deeply stained, radial nerve between the 

 tube feet and below the radial water tube. 



4. The perihsemal canal, divided by a thin partition, that lies 

 between the radial water tube and the radial nerve. 



Make a drawing of a section of an arm that will show these 

 points. 



Understand how a starfish can open an oyster or a mussel 

 and how it digests it when open. How can it digest a barnacle 

 or a small snail ? How does it respire ? 



Chadwick, H. C: Memoir No. 25. Asterias. Liverpool Marine Biol. 



Committee, 1923. 

 Cole: Experiments on Coordination and Righting in the Starfish. Biol. 



Bui., 24, 1913. 

 : Direction of Locomotion in Starfish; Asterias forbesi:. Jour. Exp. 



Zool., 14, 1913. 

 Field: Larva of Asterias vulgaris. Quart. Jour. Mic. Sci., 34, 1892. 

 Gemmill, J. F. : The Development and Certain Points in the Adult Struc- 

 ture of the Starfish, Asterias rubens. Phil. Trans, of the Royal Society 



of London, Series B, vol. 205, 1914. 

 Hopkins, A. E. : On the Physiology of the Central Nervous System in the 



Starfish, Asterias tenuispina. Jour. Exp. Zool., vol. 46, No. 2, 1926. 

 Jennings: Behavior of the Starfish Asterias forreri. Univ. Calif. Pub. 



Zool., 4, 1907. 

 MacBfide: Development of Asterias gibbosa. Quart. Jour. Mic. Sci., 38, 



1896. 

 Mead: The Natural History of the Starfish. Bui. U. S. Fish Com., 1899. 

 Tennent and Hogue: Studies on the Development of the Starfish Egg. 



Jour. Exper. Zool., 3, 1906. 



OPHIUROIDEA. 



OPHIURA. (Serpent-Star.) 



These animals live more or less concealed in crevices, shells, 

 eel-grass, etc., and may be obtained either by dredging or by 

 pulling a dip-net through eel-grass. They are not conspicuous 

 objects along the shore, as are starfish, and they differ essen- 

 tially from starfish in their method of locomotion and their 

 method of feeding. 



Examine a specimen and notice: 



1. The appearance of the disk and arms. Are the spines 

 similar to those of Asterias? The arms are more flexible. In 

 what direction do they bend easiest? 



