Experiments on the Noctiluca niiliaris. 409 



by what power so fine and hair-like a member can be made to 

 oppose such resistance to the water, as that the comparatively 

 large globular mass composing the body of the animal should 

 be drawn to it, rather than that it should pass to the globe, 

 J am unable to determine with precision, and consequently 

 refrain from offering a merely conjectural opinion. 



The method of examination which I have found to be the 

 most convenient, and from which the foregoing description is 

 taken, is to pour a small quantity of the luminous water into 

 a watch-glass and then submit it to the microscope, by which 

 means the little animals still remain floating in the water, and 

 their movements, under the eye of the observer, are in no way 

 interfered with. Examined in this manner, there is nothing 

 to be discovered to indicate any special luminous organ, or 

 the precise part of the animal devoted to the production of the 

 light; but in several specimens I could clearly observe a mass 

 of loose flocculent mucus adhering to the part which has been 

 described as being puckered in, and more immediately near 

 the insertion of the tentaculum; so that I am disposed to 

 believe that the phosphorescent principle resides in this mucus, 

 and is probably most vivid at the moment of its secretion, the 

 secretion itself appearing to be influenced and thrown out 

 more abundantly under circumstances indicating danger, 

 serving thus to account for the brilliancy with which the light 

 is manifested on first agitating the water after it has been 

 allowed to remain some time at rest. It seems probable, also, 

 that the motion of the tentaculum may at tifnes contribute 

 somewhat to the effect, by disturbing the mucus, and thus 

 bringing a newly-exposed surface of it into contact with the 

 water ; the occasional scintillations to be witnessed, even where 

 the water is under circumstances of perfect repose, being, in 

 all probability, thus produced. 



The extreme minuteness and delicacy of this little animal 

 (its natural size being stated not to exceed the jo^ooth part of 

 an inch in diameter), have no doubt been the causes that have 

 interfered to prevent its attracting any great share of popular 

 attention ; and which have also occasioned its being frequently 

 overlooked, as formerly stated, even by scientific observers. 

 Thus, in the passage formerly quoted from the work of Mr. F. 

 D. Bennett, he mentions that a bucket of water which had 

 been taken up, " though thickly studded with luminous points, 

 contained no tangible bodies ;" there can be little doubt that 

 these " luminous points " were in reality due to the presence 

 of these minute Noctilucae ; and the same remark may also 

 be extended to a similar passage which occurs at p. 321, vol. ii. 

 of the same work. In some cases, on the other hand, it would 



