ON THE STRUCTURE OF NOCTILUCA MILIARIS. 53 



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, 1, 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. Sj"). 



The oral aperture leads into the granular mass of the ali- 

 mentary cavity, from which the fibres and fibrils radiate. 

 Quatrefages says ; — 



" At one part of the groove of whicli 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 

 diiBculty. When this has been done these foreign bodies are seen to have 

 simply adhered to a semi-transparent, graunhir substance, wliich projects 

 like a hernia, so to say, from a Httle 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. 



" However carefully I have sought for a digestive canal of any kind, I 

 have never been able to discover anything of the sort ; but I have very 

 frequently seen more or less considerable vacuoles in the midst of this 

 substance. It is these most probably which have been regarded as 

 stomachs by MM. de Blainville and Suriray." 



I have never seen this projecting mass nor any foreign 

 bodies in the position indicated by Quatrefages, in perfectly 

 fresh specimens. In those which had undergone alteration, 

 on the other hand, such an appearance was frequent, but it 

 invariably appeared to me to result from a partial extrusion 

 of the contents of the stomach. 



The appearance of ' vacuoles,' on the other hand, is almost 

 invariable in fresh specimens ; but I cannot think that these 

 clear spaces, which are defined by a well-marked membra- 

 nous wall, have any analogy with the shifting ' vacuoles' of 

 the Infusoria and Rhizopods. It appeared to me, on the other 

 hand, that the oral cavity led directly in a definite stomach, 

 whose walls are capable of very great local dilatation, such 

 dilatations, connected by very narrow pedicles with the central 

 cavity, then having all the appearance of independent vacuoles 

 (fig. 3 e). The accumulation of granules around the ceniral 

 mass greatly contributes to this appearance. Like Krohn, 

 I frequently noticed large Diatomaceae and other foreign 

 matters in these gastric pouches. 



Not only does all I have observed lead me to believe that 

 Noctiluca has a definite alimentary cavity, but I am, as I 

 have said above, inclined to think that this cavity has an 

 excretory aperture distinct from the mouth. The funnel-shaped 

 depression in the post-oral area, in fact, always appeared, 

 when I could obtain a fav^ourable view, to be connected with 

 a special process of the stomach. On one occasion I observed 



