GENUS NOCTILUCA. 397 



GENUS I. NOCTILUCA, Suriray. 



Animalcules free-swimming, subspherical, consisting of a smooth, hyaline 

 investing pellicle and an internal protoplasmic mass, which radiating in 

 every direction from the centre of the body, spreads itself in a thin 

 peripheral layer over the inner surface of the bounding membrane ; the 

 oral aperture situated at the base of a subcentral infundibulate pit-like 

 depression, the single slender vibratile flagellum originating from within its 

 cavity ; a supplementary long, flexible, and elastic tentaculiform appendage 

 arising close to and overhanging the oral fossa. Endoplast conspicuous ; 

 no contractile vesicle as yet observed. HAB. Salt water. 



It has been suggested that the tentacle-like appendage in this generic type finds 

 its homologue in the frequently larger trailing flagellum or gubernaculum of 

 Anisonema and its allies, and under which circumstances the rightful position of the 

 form would be among the Dimastigous section of the present group. Having 

 respect, however, to the new generic group Lcptodiscw, in which there is no such 

 appendage, the author is disposed rather to regard this last-named structure as an 

 entirely adventitious growth. Further investigation may not improbably establish 

 a bond of affinity between Noctiluca and the correspondingly pelagic Peridiniidae, 

 certain of which, such as Gymnodinium, are devoid of an investing cuirass, while 

 many are notable in a like manner for their phosphorescent properties. 



Notiluca miliaris, Suriray. PL. I. FIGS. 34-44. 



Body hyaline, peach-shaped, somewhat compressed, with a distinct 

 meridional groove ; oral fossa situated at one extremity of the meridional 

 groove, having on one side a hard, tooth-like, projecting ridge, close to one 

 end of which the vibratile flagellum takes its origin ; tentaculate appendage 

 transversely striate, its length about equal to the diameter of the body ; a 

 narrow ridge or rod-like induration of the cuticular membrane extending in 

 a straight line from the aboral extremity of the meridional groove through 

 about one-third of the circumference of the body, and there terminating 

 abruptly. Endoplast oval, subcentral. Diameter 1-80" to 1-20". 



HAB. Pelagic, cosmopolitan ; eminently phosphorescent. 



As remarked by Professor Allman, there is perhaps no one of the phosphorescent 

 animals as yet known to science that possesses such highly luminous properties as 

 Noctiluca miliaris. To the presence of this animalcule in countless myriads upon 

 the upper stratum of the water on calm summer nights is due especially that diffused 

 form of phosphorescence that is more essentially characteristic of temperate latitudes. 

 Under the most favourable of these conditions the waves falling upon the strand 

 leave as they retreat a glittering carpet of scintillating points, the oars of the 

 passing boat seem to dip as it were into molten silver, while on the high seas the 

 waste of waters churned into foam by the revolving screw or paddles of the steam- 

 vessel leaves in its wake a broad luminous track as far as the eye can reach. A 

 glassful of water taken from the surface of the sea at such times immediately reveals 

 the origin of this wonderful phenomenon ; here and there will be seen floating 

 minute, bladder-like, transparent spheres, resembling as nearly as possible small 

 granules of boiled sago, and which exhibit on closer investigation with the micro- 

 scope, the structural characters given in the foregoing diagnosis. Irritated by 

 agitation in any shape or form they at once respond by, as it were, angry flashes 

 of silvery greenish light, and it is to the coruscations in their aggregate condition of 



