134 PROTOZOA chap. 



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 cyto- 

 plasm 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 25 6 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. 1 

 In this state the zoospore is, to all outward view, a naked Dino- 

 flagellate, whence it seems that the Cystonagellates 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. ( T V0 m 

 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 con- 

 tinuous, but weak, light. This light is so weak that several tea- 

 spoonsful 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 cyto- 

 plasm. 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 : 2 " 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 



1 See Doflein, in Zool. Jahrb. Anat. xiv. 1900, p. 1. 2 London, 1753, 402-403. 



