{134}The nucleus passes towards the surface, undergoes successive fissions, and as division goes on the numerous daughter-nuclei occupy little prominences formed by the upgrowth of the cytoplasm of the upper pole. The rest of the cytoplasm atrophies, and the hillocks formed by the plasmic outgrowths around the final daughter-nuclei become separate as so many zoospores (usually 256 or 512); each of these is oblong with a dorsal cap-like swelling, from the edge of which arises a flagellum pointing backwards; parallel to this the cap is prolonged on one side into a style also extending beyond the opposite pole of the animal.[147] In this state the zoospore is, to all outward view, a naked Dinoflagellate, whence it seems that the Cystoflagellates are to be regarded as closely allied to that group. _Leptodiscus_ is concavo-convex, circular, with the mouth central on the convex face, 1-flagellate, and attains the enormous size of 1.5 mm. (1/16") in diameter. The remarkable phosphorescence of _Noctiluca_ is not constant. It glows with a bluish or greenish light on any agitation, but rarely when undisturbed. A persistent stimulus causes a continuous, but weak, light. This light is so weak that several teaspoonsful of the organism, collected on a filter and spread out, barely enable one to read the figures on a watch a foot away. As in other marine phosphorescence, no rise of temperature can be detected. The luminosity resides in minute points, mostly crowded in the central mass, but scattered all through the cytoplasm. A slight irritation only produces luminosity at the point touched, a strong one causes the whole to flash. Any form of irritation, whether of heat, touch, or agitation, electricity or magnetism, is stated to induce the glow. By day, it is said, _Noctiluca_, when present in abundance, may give the sea the appearance of tomato soup. The earliest account of Noctiluca will be read with interest. Henry Baker writes in _Employment for the Microscope_:[148]—"A curious Enquirer into Nature, dwelling at Wells upon the Coast of Norfolk, affirms from his own Observations that the Sparkling of Sea Water is occasioned by Insects. His Answer to a Letter wrote to him on that Subject runs thus, 'In the Glass of Sea Water I send with this are some of the Animalcules which cause the Sparkling Light in Sea Water; they may be seen by holding {135}the Phial up against the Light, resembling very small Bladders or Air Bubbles, and are in all Places of it from Top to Bottom, but mostly towards the Top, where they assemble when the Water has stood still some Time, unless they have been killed by keeping them too long in the Phial. Placing one of these Animalcules before a good Microscope, an exceeding minute Worm may be discovered, hanging with its Tail fixed to an opake Spot in a Kind of Bladder, which it has certainly a Power of contracting or distending, and thereby of being suspended at the Surface, or at any Depth it pleases in the including Water.'"