354 (^N THE STRUCTURE OF NOCTILUCA MILIARIS 



and then suddenly withdrawn. Krohn, who first discovered this 

 singular organ, considers that it plays an important part in sweeping 

 nutritive matters into the oral cavity, and there can be little doubt 

 that such is the case. I would warn future observers not to be easily 

 discouraged in their search for this organ. I had sought for it in at 

 least fifty individuals without success ; and nothing but the firm 

 confidence in M. Krohn's accuracy, with which frequent working over 

 his ground has inspired me, led me to persevere until I had discovered 

 it. Among the great numbers of Noctiluc(2 which I examined, 

 however, I did not observe half a dozen which presented a good view 

 of the ciliitiii. 



Under these circumstances, I do not comprehend how it is that 

 M. Krohn should have overlooked a very remarkable structure which 

 requires no such sharpness of vision as that to which I have just 

 alluded. I refer to an S-shaped ridge arising close to the right 

 extremity of the anterior oral margin above described, and passing 

 down on the right side of the oral aperture to form its lateral and 

 posterior boundary. 



This ridge is horny-looking, and is considerably produced in its 

 middle portion into a tricuspid prominence (fig. \d\ for which I know 

 of no better name than a ' tooth.' This tooth is about i -7000th in. 

 high ; its middle cusp is stronger than the other two, and bifid, while 

 the posterior has a slight pointed heel. I have never observed any 

 movement in this tooth-like body. 



Behind it the oral aperture narrows to inclose what may be termed 

 a post-oral space, and then widens again ; the elevations bordering 

 this post-oral space are continuous with those which form the sides of 

 the triangular groove or fissure, which has been above described as 

 running up on one side of the body (figs, i, 2 b). In the midst of 

 this flattened post-oral space there is a small funnel-shaped depression 

 which I am strongly inclined to believe is an anal aperture (fig. 3/). 



The oral aperture leads into the granular mass of the alimentary 

 cavity, from which the fibres and fibrils radiate. Quatrefages says : — 



" At one part of the groove of which we have spoken, and near 

 the point of insertion of the appendage, there is always a little mass 

 of different substances, sand, &c., which can only be detached with 

 great difficulty. When this has been done these foreign bodies are 

 seen to have simply adhered to a semi-transparent, granular substance, 

 which projects like a hernia, so to say, from a little orifice (mouth of 

 authors) by which the membranes are perforated. This external 

 substance is continuous with a much larger internal mass of the same 

 nature, whose dimensions and form vary in each individual. 



