NOTES ON THE STRUCTURE OF NOCTILUCA. 331 



a deep meridional furrow extending from the pole to the 

 equator, while from the bottom of this furrow, near to its 

 equatorial end, there projects a strong vibratile flagellum. 

 It multiplies itself by transverse fission, the division of the 

 animal being always preceded by that of the nucleus which 

 thus comports itself as the cell-nucleus during cell-division ; 

 and, also, as it would seem from the observations of Krohn, 

 and, more especially, of Baddeley,^ as the nucleus of Noctiluca 

 during the spontaneous fission of this animal. 



It is true, I have not succeeded in detecting in it a mouth 

 or eferent orifice but I Avould not, on this account, insist on 

 their absence, and, under circumstances favorable for obser- 

 vation, a mouth would probably be detected at the base of 

 the flagellum. It is, moreover, ciliated on its surface, and is 

 provided with an equatorial as well as meridional furrow, and 

 with an ocelliform spot." Notwithstanding, howevei", these 

 differences, the relations between Peridinea and Noctiluca are 

 too close to be overlooked. 



There is, perhaps, not one of the phosphorescent animals 

 hitherto examined more eminently luminous than Noctiluca, 

 while the vast abundance in which this little animal occurs, 

 at certain seasons, renders it undoubtedly one of the chief 

 sources of the beautiful phenomenon of the phosphorescence 

 of the sea. At such times the sea becomes intensely lumi- 

 nous, while the Noctiluca may be then obtained in unlimited 

 quantities by means of the towing-net. 



When transferred from the net into a jar of sea water, the 

 Noctiluc(B soon rise to the surface, where they habitually 

 remain as a thick stratum, while the slightest agitation of 

 the jar in the dark will cause the instant emission of their 

 light. This is of a beautiful greenish tint, and is so vivid 

 that absolute darkness is by no means necessary to render it 

 visible, for even by ordinary lamp light it is quite perceptible. 

 The emission of the light is but of instantaneous duration, 

 and rest is needed for a repetition of the phenomenon. After 

 about a minute's repose, however, the phosphorescence may be 

 excited Avith as much vividness as before. The little animal 

 also possesses great tenacity of life, and after the slightest 



' • Quart. Journ. Mic. Soc./ vol. v, 1857, p. 185. 



- It is probable that in every case the cilia of Peridinea are confined to 

 definite tracts of its surface. Such appears, at least, to be the case in the 

 species referred to this genus by Ehrenberg. It is further probable that 

 along the ciliated tracts the structureless external sac is deficient, and that 

 the protoplasm is here naked. To suppose that the cilia arise from the outer 

 structureless cell-wall is coutrary to all we know of the nature and relations 

 of those bodies. 



