unlike itself, and this second generation would reproduce, not its kind, but the first generation; such an alternation of generations he stated to occur among the salps.  Huxley had an excellent opportunity to study this question at Cape York in November, 1849.  “For a time the sea was absolutely crowded with Salpae, in all stages of growth, and of size very convenient for examination.”  He was able to verify the general truth of Chamisso’s statement.  The aggregate form of Salpa always gives rise to the solitary salps, and the solitary salps always give rise to chains of the aggregate salps.  But the process of reproduction he shewed to be quite different in the two cases.  The solitary salp produces in its interior a little stolon or diverticulum which contains an outgrowth from the circulatory system, and this stolon gradually becomes pinched off into the members of the chain of the aggregate form.  The salps of the aggregate form are therefore merely buds from the solitary form, and are not produced in the ordinary way, by sexual generation.  On the other hand, each salp of the chain has within it 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 solitary 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 observers 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 zooelogical 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 phosphorescence.

“The sky was clear but moonless, and the sea calm; and a more beautiful sight can hardly be imagined than that presented 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 Pyrosomata floated deep, and it was only with difficulty that some were procured for examination and placed in a bucketful of sea-water.  The phosphorescence was intermittent, periods of darkness alternating with periods of brilliancy.  The light commenced in one spot, apparently on the surface of one of the zooeids, and gradually spread from this as a centre in all directions; then the whole was lighted up:  it remained brilliant for a few seconds, and then gradually faded and died away, until the whole mass was dark again.  Friction