Sponges and Animalcules 



767 



Photo by W. Saville-Kcnt, F.Z.S.] [Milford-on-Sea. 



SHELLS OF FORAMS HIGHLY MAGNIFIED. 



The chalk cliffs of Dover and many other strata are mainly 

 composed of similar microscopically minute shells. 



countless myriads upon the upper stratum of 



the water on calm summer nights that is 



especially due the diffused form of phosphor- 



escence which is more essentially characteristic 



of temperate latitudes. Under the most favour- 



able 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 as it were to dip into molten 



silver ; while on the high seas the revolving 



screw or paddle 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 sea 



at such times immediately reveals the origin of 



these wonderful phenomena. Here and there will 



be seen floating minute bladder-like transparent 



spheres, resembling as nearly as possible small 



granules of boiled sago. Investigated more 



closely with the microscope, each individual 



speck will be found to exhibit a pouch-like 



contour, having a central furrow, from the which 



lash projects, and upon which the minute mouth- 



aperture opens. Irritated by agitation in any shape or form, the Noctilucas at once respond 



by, as it were, angry flashes of silvery-greenish light, and it is to the coruscations in their 



aggregate condition of many millions of these minute organisms that the several phenomena 



above recounted are produced. 



One other characteristic manifestation of ocean phosphorescence dependent upon the 

 presence in countless numbers of these minute animalcules may be recorded. To those 

 accustomed to a seafaring life the spectacle is a common one, on nights when the luminosity 

 is most in evidence, of fishes following or darting away from the sides of the vessel apparently 

 aglow themselves with phosphoric light, and leaving behind them, in accordance with their 

 size, a more or less conspicuous luminous path in 

 the murky waters. It is commonly supposed that 

 such form of luminosity is emitted by the fishes 

 themselves ; but on closer investigation it will be 

 found that this also is due to the presence of 

 the animalcules under notice in countless numbers, 

 which are disturbed into a sudden display of 

 their phosphoric properties by the passage of the 

 fishes through their midst. This light is reflected, 

 as from a mirror, by the fishes' glittering scales, 

 while the Noctilucas continue scintillating for 

 several seconds in the path or wake through 

 which the fishes have passed. 



There are other animalcules nearly allied to 

 Noctilucas which sometimes occur in such vast 

 abundance in both salt and fresh water as to 

 visibly affect its character. In addition to a very 

 long lash they have a girdle of vibratile hairs. 

 The fresh-water representatives of this group are 

 sometimes brilliant green, at others bright scarlet. 

 That instance among the Biblical Egyptian plagues 







bavMc-Kent, F.Z.S.] [ATilford-on-Sea. 



NOCTILUCAS. 



These are the animalcules which chiefly produce marine phospl 

 escence. 



