198 THREE CRUISES OF THE “ BLAKE.” 
dark night, when the motion of 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 marie 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 Pyrosom:e, 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 
naturalists who have sailed through 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 Salpæ 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, siphonophores must be very nu- 
merous. Ја the roadstead under the lee of the islands there is 
little pelagie life. Everything either remains at a short dis- 
tance below the surface, or is blown away to seaward of the 
