FIXED LUMINARIES OF THE SEA. 21 



to the shells of hermit crabs; and, if luminous, we may- 

 imagine the spectacle of the gleaming, living light-house, 

 moving about at the will of the little crustacean, possibly- 

 attracting prey to it instead of being the warning beacon 

 that we might suppose. The anemones being, as a rule, fixed, 

 one naturally likens this one to a light-ship which is drifting 

 about away from its moorings. 



The sea-anemones well repay examination and study, and 

 thrive well in the aquarium, where their habits and develop- 

 ment may be watched. As a rule, they are fastened to the 

 rocks by a sucking disk. Some live in the mud ; others float 

 upon the surface, or are parasitic upon the great jelly-fishes. 

 Some, as we have seen, ride about upon hermit crabs, or 

 fasten themselves upon the claws of others; thus showing 

 the greatest diversity in their life habits. The corals may 

 be termed anemones which have the faculty of secreting 

 or depositing lime, and among them are several which at 

 times appear phosphorescent. The little cup-like Caryophyl- 

 lia has been seen to emit a gleam of light, an idea of which is 

 given in Plate III., Fig. 2. 



The phosphorescence of reef-building corals has rarely 

 been observed. Col. Nicolas Pike, our late consul to Mauri- 

 tius, and an enthusiastic naturalist, informs me that he has 

 witnessed the luminosity of their young. The account is 

 so interesting an addition to the literature of the subject in 

 general, that I give the colonel's letter entire : — 



Brooklyn, N.Y., December, 1886. 



Dear Mr. Holder, — I remember on one occasion, -when sailing 



on the Indian Ocean, the night -was dark, but the crest of every wave 



glowed with light. As our vessel moved swiftly through the water, 



dashing the foamy waves on each side of her bows, she left bright streaks 



