ON THE STRUCTURE OF NOCTILUCA MIIJARIS. 51 



Noctiljica appear to push repeatedly against obstacles, with 

 this tentacle. 



The body is composed of a structureless and somewhat 

 dense external membrane, which is continued on to the 

 tentacle. Beneath this is a layer of granules or rather a 

 gelatinous membrane, through whose substance minute gra- 

 nules are scattered without any very definite arrangement. 

 From hence arises a network of very delicate fibrils, whose 

 meshes are not more than l-3000th of an incli in diameter 

 (fig. 6), and these gradually pass internally, — the reticulation 

 becoming more and more open — into coarser fibres, which 

 take a convergent direction towards the stomach and nucleus. 

 All these fibres and fibrils are covered with minute granules, 

 which are usually larger towards the centre. 



Quatrefages states that these granules may be seen to glide 

 from the centre to the circumference, and vice versa, propelled 

 by the contractions or expansions of the transparent matrix 

 in which they are imbedded ; that new fibrous processes 

 (expansions) arise on the central mass and unite, dividing and 

 subdividing, with the neighbouring ones — and that if the 

 creature be irritated, the fibres and fibrils become detached 

 from the investing membrane, and are drawn in towards the 

 mouth " like threads of a very viscid liquid, which retract 

 slowly after being broken." 



All these appearances may be very readily seen ; but I am 

 strongly inclined to believe that the greater part of them are 

 abnormal states, and that in their natural and perfectly un- 

 altered condition, the fibres and fibrils are perfectly quiescent, 

 and present notliing to be compared with the protean move- 

 ments of the Am(Bb(B. In their perfectly fresh and unchanged 

 state, in fact, the fibrous network is by no means so obvious 

 as it usually appears, and in such specimens 1 have been 

 unable to convince myself that the granules undergo any 

 change of place — certainly there is no protrusion and retrac- 

 tion of processes to be compared with that which takes place 

 in the Rhizopoda.* 



The oral aperture has been satisfactorily described by 

 Krohn. Supposing the animal to lie upon its oral face (the 

 attitude it commonly assumes), with its tentacle forwards — 

 the oral aperture appears as a sort of half oval, with a nearly 

 straight edge anteriorly, and a deeply-curved outline pos- 

 teriorly (fig. 4). 



* Krohii states, that he could hardly ever cause the Noctilucce to con- 

 Iract by mechanical or chemical irritation; but that he once saw one 

 which repeatedly contracted before falling into the permanently wrinkled 

 and collapsed condition, into which they so readily pass. 



£ 2 



