SPONGES AND ANIMALCULES 



767 



Phot, by W. Savillt-Kent, F.Z.S.] \_Milftrd-tn-St* 



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 trans- 

 parent 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 which the 

 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 





fhtti b } IV. Savillt-Ktnt, F. Z.S.I 



NOCTILUCAS 



iMilferd-tn-Sta 



These are the animalcules 'which chiefly produce marine 

 phosphorescence 



