MONOGRAPH OF THE EXISTING CRINOIDS. 609 



NOTES ON THE HABITS OF ANTEDON. 



Prof. A. Milnes Marshall, who studied Antedon mediterranea at Naples, says 

 that the normal position of the animal is a fixed one, the animal being attached by 

 the cirri to some foreign body and the arms spread out horizontally with their tips 

 slightly flexed. The oral pinnules are bent over the disk, crossing one another above 

 it; the other pinnules are spread out nearly at right angles to the arms. In an 

 aquarium containing a large number of specimens the great majority will be found 

 attached either to the bottom or sides of the tank with the oral surface directed 

 either upward or more or less obliquely ; some specimens, however, are almost cer- 

 tain to be found, if there be foreign bodies in suitable positions for attachment, 

 inverted, with the oral surface downward. A comatulid when attached exhibits 

 very little tendency to alter its position, and may remain fixed in the same place 

 for weeks. If detached, either spontaneously or by force, it can, and usually does, 

 swim actively until it reaches a suitable place of rest to which it anchors itself by 

 its cirri. The normal swimming movements, which are peculiarly graceful, consist 

 in strong flexion of the proximal half of the arm, which is raised vertically over 

 the disk, and then extension of the whole arm, the distal half of which is thrown out 

 something like a whiplash. During flexion the pinnules are folded alongside the 

 arm, during extension spread out so as to expose as great a surface as possible. 

 Usually two or three arms are raised simultaneously, sometimes as many as five, 

 but the only rule seems to be that the two arms of each pair are always flexed 

 alternately. When the animal is attached the arms exhibit but very slight move- 

 ments ; they are usually spread widely out, apparently to expose as large a surface 

 as possible. If an animal be detached and placed with the oral surface downward 

 it will right itself almost at once. If the surface on which it is placed be a rough 

 one the righting movement is effected in a few seconds, or almost instantaneously. 

 In a glass vessel it takes longer to perform, though never over two minutes in an 

 active individual. 



In regard to the ordinary condition of the arms of Antedon bifida W. B. Car- 

 penter noted that there is much the same variety as is seen among actinians with 

 respect to the expansion of their tentacles. Sometimes the arms and their pinnules 

 are stretched out quite straight to their full length, and almost entirely in the same 

 plane, so as to present an appearance of rigidity, while sometimes, still remaining 

 fully extended, they are more or less closed together so as to give their whole ex- 

 panse the shape of a funnel more or less deep with the central disk at its bottom. 

 More commonly, however, some of the arms curve either obliquely or toward the 

 ventral surface, and this ventral curvature may be so great that the arm forms a 

 spiral, which reminds the observer of the unfolding frond of a fern. Occasionally 

 all of the arms are seen to be thus coiled, so that the diameter of the animal is 

 reduced to not more than one-third of that which it has when the arms are fully 

 extended. In no instance did Carpenter see the arms more than slightly curved 

 dorsally. 



"W. B. Carpenter noticed that if one of the middle or outer pinnules of any arm 

 be irritated by the contact of a rod, such irritation merely produces a languid 

 wavy motion of the arm thus acted on, which may extend itself to others if the 



