MOLLUSCOiDA. 3L3 



This was a broad and extensive sheet of phosphorescence extending 

 from east to west as far as the eye could reach. I immediately cast 

 the towing-net over the stern of the ship, which soon cleaved through 

 the brilliant mass, the disturbance causing strong flashes of light to 

 be emitted, and the shoal, judging from the time the vessel took in 

 passing through the mass, may have been a mile in breadth. On 

 taking in the towing-net, it was found half filled with Pyrosoma 

 ailanticum, which shone with a beautiful pale greenish light. After 

 the mass had been passed through by the ship, the light was still 

 seen astern, until it became invisible in the distance, and the ocean 

 became hidden in the darkness as before this took place. 



" The second occasion of my meeting these creatures was in a high 

 latitude, and during the winter season. It was on the 19th of August, 

 the weather dark and gloomy, with light breezes from north-north- 

 east, in lat. 40 30' S., and 138 3' E. long., at the western entrance 

 to Bass's Straits, and about 8 o'clock P.M., when the ship's wake was 

 perceived to be luminous, while scintillations of the same light were 

 abundant all round. To ascertain the cause, I threw the towing-net 

 overboard, and in twenty minutes succeeded in capturing several 

 Pyrosoma, which gave out their usual pale green light ; and it was, 

 no doubt, detached groups of these animals which were the occasion 

 of the light in question. The beautiful light given out by these 

 molluscans soon ceased to be seen; but by moving them about it 

 could be reproduced for some length of time after. The luminosity 

 of the water gradually decreased during the night, and toward morn- 

 ing was no longer seen." 



The genus Scdpa forms another interesting group of Tunicata. 



The Biphora or Salpa (Fig. 12 6) are long transparent threads of the 

 more delicate tissues, composed of rows of individuals placed side by 

 side, and grafted, as it were, transversely : ribbons, in which each 

 animal is grafted end on end to its sister : double parallel chains of 

 social creatures, sometimes alternate, sometimes opposite ; living chap- 

 lets, of which each pearl is an individual. Each individual presents 

 an oblong diaphanous or prismatic body, more or less symmetrical, 

 and often furnished in front, rarely behind, with tentaculiform ap- 

 pendages. So great is the transparency, that the various organs may 

 be observed through the skin as they perform their several functions. 



Momus, an ancient philosopher, thought it a subject of regret that 



