110 Papers from the Department of Marine Biology. 



small Comatella maculata, which, after wearing the cork float in the 

 live-car for 24 hours, was dropped into deep water. It immediately 

 began swimming, but spasmodically and not in the beautifully coordi- 

 nated manner of a Stephanometra. Apparently these comasterids do 

 not, under normal conditions, swim at all, but could with sufficient 

 effort be taught to do so. 



On the other hand, all of the species of the other families of comat- 

 ulids observed at Maer are good swimmers and do not creep about as 

 the comasterids do. They are usually found at rest on the lower side 

 of rock-fragments or on a branch of coral with the arms more or less 

 erect, but sometimes the arms are opened out flat against the rock. 

 They maintain their position by means of the cirri, with which they 

 often cling so tightly that it is difficult to dislodge them without 

 damage. Under no conditions did they seek to escape by swimming, 

 but when once dislodged, swimming seemed to be their only means 

 of locomotion. Placed in a basin or a deep bucket of sea-water, a 

 very slight mechanical stimulus served to set them in motion, and 

 swimming continued for a more or less brief interval, varying greatly 

 with different individuals. It seemed as though the frequent contact 

 with the side of the basin or pail served as a deterrent, and I think 

 that they would undoubtedly have gone a greater distance in open 

 water. Nevertheless it was clear that the individuals observed were 

 "sprinters," and not long-distance swimmers, the movements being 

 more like the flitting of small birds in shrubbery than like long-sustained 

 flight. The gracefulness and beauty of the movements were their most 

 notable feature, but their rapidity and force were also remarkable. 



In the ten-armed specimens, swimming was accomplished by using 

 the arms in sets of five alternately, so that when arms 1, 3, 5, 7, and 



9 were brought up almost vertically over the disk, arms 2, 4, 6, 8, and 



10 struck backward forcibly, with pinnules fully extended, until they 

 nearly met behind the cirri. Only a single stroke was made, but as 

 arms 2, 4, 6, 8, and 10 were relaxed and drawn in and upward over the 

 disk, another similar stroke was made by the alternating five arms. 

 Of course the movement was much more rapid than a description indi- 

 cates, but it decreased in rapidity as the comatulid became fatigued. 

 At the start the strokes were at the rate of perhaps 100 per minute, 

 but they rapidly dropped to much less than that and usually ceased 

 altogether in less than a minute. Each stroke appeared to carry the 

 individual about the length of its own arms, so that an individual with 

 arms 50 mm. long started out at the rate of about 5 meters per minute. 

 But the longest distance any specimen was seen to travel continuously 

 was less than 3 meters. 



In the multibrachiate Stephanometridse and Mariametridae, the 

 movements were very similar, but exceedingly difficult to analyze 

 satisfactorily. The arms seemed to be used in sets of five in rapid 



