60 Papers from the Marine Biological Laboratory at Tortugas. 



eggs, it has a much longer pelagic life than the Alpheid and is much more 

 likely to be eaten or swept out to sea by the tides, where it can not find 

 a sponge when the proper time comes. 



The smallest loggerhead sponges I found would not live in a large 

 aquarium with running sea-water more than 2 days before the water 

 began to get foul within the passages in the sponge and the Alpheids 

 and Typton began to die. Field observations were very limited. These 

 and other difficulties restricted the investigation to its present limits. 



ON ADAPTATIONS OF THE REEF ANEMONE, CRADACTIS VARIABILIS. 



Cradactis variabilis Hargitt is an anemone about an inch or two in 

 length when expanded, living in holes in old coral heads or reef rocks. 

 Besides the tentacles, which are few in number and arranged as in Sagar- 

 tia, long outgrowths called fronds extend from the region bearing the 

 tentacles (plate i, figs. 4, 5; plate 2, figs. 8, 9, 10). The animals may be 

 a moss-green or brown in general color, but the tentacles are always 

 paler and often colorless and transparent at their tips. The fronds may 

 or may not be branched, and may end simply or in pale knobs, as in 

 plate I, fig. 4, or in curious "eyes," as in fig. 5. 



These anemones are usually found in cavities in old coral heads that 

 communicate with the exterior by a number of passages about half an 

 inch or more in diameter. The anemones are attached near enough to 

 these passages to extend the tips of the fronds to the exterior (plate 2, 

 fig. 7). This extension is caused by heliotropism of the fronds. One 

 mistakes them at first for sea-weed, although they do not resemble any 

 particular kind of sea-weed that I have found growing on the reefs. 

 The tentacles are extended about as far as and sometimes a little farther 

 than the fronds, but the fronds tend to conceal the tentacles. At night 

 the fronds are contracted and the tentacles remain extended; therefore 

 it is probable that the fronds are not necessary as breathing organs. 



If a bit of crab meat is held near the passage through which the 

 Cradactis is extended no response is obtained. But if one of the fronds 

 is touched with the meat the tentacles are extended toward it, while the 

 frond touched may contract slightly. In order to observe the food- 

 taking more minutely, some of the anemones were taken from the rock 

 and allowed to attach themselves to the bottom of an opaque dish filled 

 with sea-water. When a bit of crab meat is placed on the end of a ten- 

 tacle it adheres and the tentacle and one or more adjacent ones are bent 

 down and the food placed on the mouth and pressed there. Immediately 

 many or all of the tentacles are pressed on the food, hiding it from view 

 until it is swallowed. The fronds may contract more or less during 

 the process. Cradactis sometimes swallows filter paper placed firmly on 

 the mid-region of a tentacle or on the disk, but not when placed on the 

 end of a tentacle. This may be a question of degree or extent of stimu- 

 lation. It disgorges the paper within 10 minutes. It rejects bits of shell, 

 etc., placed on the disk or tentacles. 



India ink placed in the water near the anemone showed ciliary 

 currents running towards the tips of the tentacles and fronds, and on 



