the class from which it has itself so lately emerged.  At this point there is a halt.  The medusa remains in its polype state for some months.  At the expiration of this term, a strange alteration in its appearance begins to take place.  Rings are formed round its body, from ten to fifteen in number.  These gradually deepen, until at length it is literally cut up into a number of segments, which rest one upon the other—­their upper margins becoming elevated, and divided into eight lobes.  It is, in fact, a pile of cup-shaped pieces, very loosely connected together.  A little later, these pieces free themselves successively, and the sedate polype disappears in a company of sprightly young medusae.  These beings, indeed, still differ in some respects from the adult animal; but the differences gradually vanish, and we have the perfect jelly-fish as the final result of this extraordinary series of transformations.

Similar observations have been made respecting other tribes amongst the lower animals, and some interesting generalisations have been founded upon them, into which, however, it is not our present purpose to enter.

The Acalephae are the principal agents concerned in the production of the beautiful phenomena of phosphorescence.  The minute species—­mere gelatinous specks—­swarm at times by countless myriads in the waters of the ocean, and make its surface glow with ‘vitalised fire.’  The waves, as they curl and break, sparkle and flash forth light, and the track of the moving ship is marked by a lustrous line.  ’In the torrid zones between the tropics,’ says Humboldt, ’the ocean simultaneously develops light over a space of many thousand square miles.  Here the magical effect of light is owing to the forces of organic nature.  Foaming with light, the eddying waves flash in phosphorent sparks over the wide expanse of waters, where every scintillation is the vital manifestation of an invisible animal world.’  Beneath the surface larger forms are seen, brilliantly illuminated, and lighting up the mystic depths of the sea.  Fiery balls and flaming ribbons shoot past; and submarine moons shine with a soft and steady light amidst the crowds of meteors.  ’While sailing a little south of the Plata on one very dark night,’ says Mr Darwin, ’the sea presented a wonderful and most beautiful spectacle.  There was a fresh breeze; and every part of the surface, which during the day is seen as foam, now glowed with a pale light.  The vessel drove before her bows two billows of liquid phosphorus, and in her wake she was followed by a milky train.  As far as the eye reached, the crest of every wave was bright; and the sky above the, horizon, from the reflected glare of these livid flames, was not so utterly obscure as over the vault of the heavens.’  Even in our own seas very beautiful displays of phosphorescence may be witnessed.  On fine summer nights, a soft, tender light plays round the boat as it moves onward, and the oars drop liquid fire.  For how much of beauty are we indebted to these living specks of jelly?