198 THREE CRUISES OF THE " BLAKE." 



dark night, when the motion o£ the vessel sets the sea on fire 

 around one. At such times there is something wild and weird in 

 the whole scene, which at once fascinates and appalls the imagi- 

 nation ; one seems to be rocking above a volcano, for the sea 

 is intensely black, except where fitful flashes or broad waves 

 of light break from the water under the motion of the vessel. 

 The sea may be black as ink, with the crests of the waves 

 breaking heavily and surrounding one with walls of fire in all 

 directions. 



To Professor Panceri we owe the fullest investigations as yet 

 made into the causes of marine phosphorescence. The phospho- 

 rescence is limited to portions of the exterior of the animal ; or 

 is connected with special organs, — sometimes with the gener- 

 ative organs ; or it may take place wherever tissues change rap- 

 idly. But as this power of emitting phosphorescence seems 

 to be always produced by an external irritation, it may be, as 

 has been suggested by Studer, that the phosphorescence serves 

 as a protection for the animal. 



The Pyrosomae, which form so essential a feature in the phos- 

 phorescence of the Indian Ocean, are not common in the Carib- 

 bean or Gulf of Mexico. The specimens we saw in the track 

 of the " Blake " were diminutive in comparison with those huge 

 fire cylinders, often more than a foot in length, described by 

 naturahsts who have sailed throuo-h the Indian seas. On the 

 other hand, we found a Salpa colony far exceeding in size those 

 before known, — a huge band, several yards in length and a 

 foot in breadth, which at night, when seen from the deck, 

 seemed like a huge veil of bright greenish phosphorescence. 

 One of the smaller kinds of Salpae gives out generally a bluish 

 light. 



The pelagic fauna of the Eastern Caribbean is, during the 

 winter season, rather scanty. Owing to the constant agitation 

 of the water, I had no opportunity, as in the Gulf of Mexico, 

 of making much use of the tow-net. From the number of 

 fragments constantly found, siphon oph ores must be very nu- 

 merous. In the roadstead under the lee of the islands there is 

 little pelagic life. Everything either remains at a short dis- 

 tance below the surface, or is blown away to seaward of the 



