398 ORDER FLAGELLATA-EUSTOMATA. 



millions of these minute bodies that the several phenomena above recounted are pro- 

 duced. One other manifestation of pelagic phosphorescence dependent upon the 

 presence in countless numbers of this same tiny protozoon, may be suitably recorded 

 in these pages. By those accustomed to a seafaring life, the sight on nights when 

 the luminosity of the sea is most conspicuous, of fish following or darting away 

 from the sides of the vessel, apparently themselves aglow with phosphoric light, 

 and leaving behind them, in accordance with their size, a more or less conspicuous 

 luminous path in the murky waters, is frequently recorded. It is commonly sup- 

 posed that such form of luminosity is emitted by the fish themselves, but on closer 

 investigation it will be found that this also is due to the presence of the animal- 

 cules now under discussion, and which are disturbed into a sudden display of their 

 phosphoric properties by the pa'ssage of the fish through their midst. This light is 

 reflected as from a mirror by the glistening scales of the larger animal, while the 

 NodihiccB remain scintillating for some few moments in the path through which the 

 fish has passed, thus producing the more or less conspicuous tracks of light which 

 are left in its wake.* 



The special seat of the phosphorescent properties of Nodiluca miliaris is pre- 

 sumed to be the peripheral protoplasmic layer lying immediately beneath the surface 

 of the cuticle. This supposition is favoured by adding a small drop of alcohol to 

 the water containing a living specimen while examined under the microscope. In 

 place of the momentary flash of light emitted under ordinary disturbance, the little 

 creature now exhibits its luminosity with the fullest intensity for several seconds. 

 At the end of that time it commences to gradually disappear, and before becoming 

 finally extinct with the Ufe of the animalcule, presents the aspect of a mere luminous 

 ring upon the dark background of the field of the microscope. This last phe- 

 nomenon is pointed out by Professor Allman as indicating that the phosphoric 

 properties are confined to the peripheral portion, the light when the annular 

 appearance is presented having become so weak as to be appreciable only towards 

 the edges of the projected sphere, and where necessarily a greater depth of the 

 luminous stratum lies in the direction of vision. On the other hand, there appears 

 to be no appreciable differentiation between the protoplasmic stratum beneath the 

 cuticle and the central or radiating portions, and it is difficult to reconcile this 

 fact with the presumed limitation of the phosphoric property. It would seem an 

 open question, indeed, whether the last peripheral scintillations of the dying 

 Nodiluca are not directly comparable with the phenomena exhibited by a burning 

 paper in which the flame, having no longer any pabulum to support its volume, 

 leaves upon its departure a multitude of coruscating sparks which, animated by a 

 mysterious and irresistible centrifugal force, hurry or creep out as it were from the 

 centre and become extinct only on reaching the periphery. If the substance of the 

 charred paper reflected and transmitted instead of absorbed light, as is apparently 

 the case with the smooth cuticle of Nodiluca, the last appearance presented in this 

 instance also, presuming the paper was circular, would be that of a luminous ring. 



The process of reproduction in Noctiluca has been successfully followed by Cien- 

 kowski.f Transverse fission after the manner common to almost all the Infusoria, 

 attended by an enlargement and division of the central nucleus or endoplast, is of 

 common occurrence. During this process the animalcule retains its normal contour 

 or assumes a spheroidal or semi-encysted form, in which all traces of the tentacle, 

 tooth-like process and cilium, and meridional groove entirely disappear, presenting, 

 indeed, under such circumstances so distinct an aspect as to have been frequently and 

 even quite recently {i)ide infra) mistaken for a separate organism. In connection with 

 this spheroidal condition, a process of multiplication is recorded by Cienkowski that 

 has not been previously observed. In this instance the central endoplast disappears 

 and the protoplasmic contents of the cyst, collecting to one spot on its inner surface. 



* A fuller reference to this special form of marine phosphorescence, as witnessed by the author 

 in the Bay of Biscay, is contained in an article on " Phosphorescence in Fish," published in ' Nature,' 

 vol. vii., for the year 1872. 



t ' Archiv f. Mikroskopische Anatomic,' Band vii. Iloft ii,, iS/i, and Band ix. Ileft i., 1872. 



