Phosphorescence 55 



a true egg-cell. This is fertilised by a male cell, and 

 within the body of the parent, nourished by the blood 

 of the parent, grows up into the sohtary form. There 

 is then an alternation of generations, but there are not 

 two sexual generations. The sexual generation of 

 chain salps gives rise to forms which reproduce by 

 buds. From this conclusion, with which all later ob- 

 servers have agreed, Huxley went on to his theory of 

 individuality. Different names had been given to the 

 two forms, but Huxley declared that neither form was 

 a true zoological individual ; they were only parts of 

 individuals or organs, and the true individual was the 

 complete cycle involving both forms. 



In addition to determining the interesting method of 

 reproduction, Huxley made an elaborate investigation 

 of the structure of Salpa. On one occasion only the 

 Rattlesnake came across a quantity of an allied Ascidian, 

 Pyrosoma, which had received its name from its phos- 

 phorescence. 



"The sky was clear but moonless, and the sea calm; and a 

 more beautiful sight can hardly be imagined than that pre- 

 sented from the deck of the ship as she drifted, hour after hour, 

 through this shoal of miniature pillars of fire gleaming out of 

 the dark sea, with an ever-waning, ever brightening, soft 

 bluish light, as far as the eye could reach on every side. The 

 Pj^rosomata floated deep, and it was only with difficulty that 

 some were procured for examination and placed in a bucket- 

 ful of sea-water. The phosphorescence was intermittent, peri- 

 ods of darkness alternating with periods of brillianc}-. The 

 light commenced in one spot, apparently on the surface of one 

 of the zooids, and gradually spread from this as a centre in all 

 directions ; then the whole was lighted up : it remained bril- 

 liant for a few seconds, and then gradually faded and died 

 away, until the whole mass was dark again. Friction at any 

 point induces the light at that point, and from thence the 

 phosphorescence spreads over the whole, while the creature is 



