MONOGRAPH OF THE EXISTING CEINOIDS. 607 



While the Albatross was anchored off Sulu a young Dorometra nana of about 

 half the adult size was captured at the surface. It was said to have been swim- 

 ming entirely by means of its cirri, with the arms widely extended. 



John Vaughan Thompson was the first to describe the locomotion of Antedon 

 bifida. He says that in swimming the movements of the arms exactly resemble 

 the alternating stroke given by the medusae to the liquid element, and has the same 

 effect, causing the animal to raise itself from the bottom and to advance, back 

 foremost, even more rapidly than the medusa. He speaks of Antedon as an animal 

 not only free, but leading the most vagrant life of any of the tribe with which it 

 has hitherto been associated by naturalists, at one time crawling about amongst 

 submarine plants, at others floating to and fro, adhering to thin fragments by 

 means of its dorsal claspers, or even swimming about after the manner of the 

 medusae. 



But of all the naturalists who have written on these animals Thompson is the 

 only one who considered Antedon as normally active. All of the species of this 

 genus appear to agree in their habits, of which the best account is that given by 

 Dr. W. B. Carpenter, based upon Antedon bifida. 



Doctor Carpenter says it is quite true that, as stated by Mr. J. V. Thompson, 

 and confirmed by Prof. Edward Forbes, an Antedon placed freely in water will 

 swim with considerable activity, moving back foremost by advancing five arms at 

 a time, and then the alternative five ; in fact, he did not know any animal of which 

 the movements are more graceful than those of the feather-star. But he is quite 

 satisfied from repeated observations that these movements are not habitual to the 

 animal and are to be regarded only in the light of a restless search aftep a new 

 attachment, being kept up no longer than is requisite for obtaining this. 



If an Antedon be placed in a large basin of sea water having smooth sides 

 and not containing any object of which the cirri can lay hold, the swimming 

 action may continue (with occasional intermissions) for several hours. But if 

 a rough angular stone, a seaweed, a zoophyte, a cluster of serpulee, or anything 

 to which the dorsal cirri can attach themselves, be placed in the basin, the Antedon 

 settles itself upon this, and if the attachment proves suitable the creature seldom 

 changes it. 



Doctor Carpenter kept a number of Antedons for several weeks together in 

 the same aquarium without any other animals, and he observed that the places of 

 individuals which he could distinguish by some peculiarity of color were scarcely 

 at all altered during the whole period, the amount of change, in fact, being little 

 more than would have been exhibited by an equal number of actinians. One fine 

 specimen he particularly noted as having firmly attached itself by the grasp of its 

 dorsal cirri to the tube of a Serpula, and this it did not let go during the whole 

 time of its captivity. 



Doctor Carpenter says that as regards the ordinary fixedness of its position 

 the condition of the adult Antedon only differs from that of its pentacrinoid larva 

 in that whereas the latter necessarily remains fixed to the spot to which the base 



