The Comatulids of Torres Strait. 115 



the arms, and the arrangement and appearance of the ciliated furrows, 

 it is evident that the comatulids at Maer obtain their food, living 

 vegetable plankton, directly from the sea-water by means of the 

 ciliated furrows and that the arms serve no essential purpose in feeding 

 other than the multiplying and extending of these furrows. 



If this view is correct, a plentiful supply of sea- water containing an 

 abundance of the necessary plankton would be the essential factor in 

 controlling the distribution of these comatulids, and their local occur- 

 rence about the island might throw some light on the matter. The 

 island of Maer is surrounded on all sides by a fringing reef between 

 which and the shore itself is a reef-flat of great extent, as much as 

 600 yards wide on the southeast side of the island. The reef is lacking 

 only at one point, the west-south-west corner of the island, but it is 

 nearly wanting at the southern point also. Between these two gaps 

 the southwestern reef is very rich in corals and in other animal life. 

 Directly across a channel, about a mile wide, lie the islets Dauer 

 and Weier, also surrounded by an extensive fringing reef. Through 

 this channel the tidal movement is very marked, spring tides at the 

 Murray Islands rising not less than 10 feet. On the southeastern 

 reef there is constant surf breaking (at least during the southeast 

 trades of the dry season), but the tidal movement on the flat itself is 

 not particularly active. At the northern end and on the west side 

 of the island, neither surf nor tide is as marked as on the other side. 



We examined the reef and the reef-flat on all sides of the island and 

 were constantly searching for crinoids. Young Comatula purpurea 

 were found practically everywhere in water that was well aerated, 

 but no large comatulids were found anywhere on either the western 

 or northern parts of the reef. On the southeast reef-flat, Comatella 

 maculata was fairly common and occasionally a Comanthus annulatum 

 or a Lamprometra would be found there; but we soon learned that 

 when we wanted crinoids in any numbers, the southwestern reef was 

 the place at which to obtain them. They occurred there in great 

 abundance, and especially near the outer margin of the reef the number 

 of species and the size of the individuals were notable. A natural 

 explanation of this fact is that the great tidal movements through the 

 channel between Maer and Dauer maintain a richer supply of vegetable 

 plankton at that point than is to be found on any of the other reefs. 

 It may be added that the abundance of food is, as will be shown later, 

 only one factor in making the southwestern reef so attractive to 

 comatulids. 



RESPONSE TO LIGHT. 



Almost the first fact noted with reference to the habits of the 

 comatulids at Maer was that they showed an evident tendency to 

 withdraw from brightly illuminated areas. On overturning a rock- 

 fragment on the lower surface of which crinoids were living, they at 

 once began to move. Sometimes they withdrew into dark holes or 



