OF NAUTILUS POMPILIUS. 25 



The second layer of tentacular processes is brought into view by cutting off the hood 

 and the external digitations. Fig. 6. PI. VIII. gives a view of this dissection. In this 

 figure b is the eye, d the funnel, as in the foregoing figure ; c, c are the cut parts of the 

 tentacles contained in the digital processes. The layer now visible is formed by that set of 

 tentacular sheaths which Professor Owen calls the external or superior labial processes 

 (fig. 6, k, k). For a reason explained in the following part of my paper, I would be dis- 

 posed to prefer the name of external labial process to that of superior. The membrane 

 covering the mandibles and the muscular mass of the mouth, and terminating in the 

 fringed lip encircling those parts, is to be seen at a little distance above this layer (at m), 

 and shows numerous circular folds. Beneath this layer a small part of the third layer 

 (/) is visible. 



This third layer is brought into view by removing the second (see fig. 7). In this 

 figure k, k are the cut parts of the tentacles of the external labial process, and / is the 

 internal or inferior labial process of the left side. The folded membrane m is now almost 

 wholly visible. The internal labial processus consists of a flattened stalk, which ascend- 

 ing expands in a compressed paddle, whose superior margin is straight and perforated 

 for the exsertion of the tentacles. There is some likeness to a glove whose fingers are 

 cut off. The description of Rumphius mentions all the digitations and processes as 

 superimposed flaps, each in shape of a child's hand'. This comparison answers chiefly 

 to the internal labial processes. 



The number of tentacles in those two pair of labial processes is not exactly the same 

 in difl^erent specimens, nor even in the same specimen at both sides. The description 

 of Rumphius gives sixteen tentacles to the external labial processes, but does not men- 

 tion their number in the internal processes. Professor Owen found twelve tentacles, 

 Professor Valenciennes thirteen in each of those four processes. In the external processes 

 ProfessorW.Vrolik observed twelve tentacles on each side, as was observed also by me. 

 The internal processes seem to have in general a somewhat larger number ; Professor 

 Vrolik observed in this layer fourteen on each side ; I found also fourteen at the left and 

 sixteen at the right side. The external labial processes are united in the mesial line at 

 the ventral side above the funnel by a membrane with numerous fine folds on the inside ; 

 the internal approach here nearer to each other and are united in a similar manner ; 

 the commissure presents on the inside, towards the dorsal surface, seventeen or eighteen 

 eminent, compressed, longitudinal folds, like the parallel ridges in the olfactory cavity 

 of Fishes. This part is, according to Professor Owen's opinion, the organ of smell ; but 

 I believe that those folds are only rudimental digitations completing the circle of the in- 

 ternal labial processes, and similar to the more numerous and smaller folds of the exter- 

 nal circle, or even to the fringed margin of the lip round the mandibles. 



In respect to the observation of Valenciennes concerning the mandibles, it is perhaps 

 not unnecessary to note that I saw them in different specimens always covered with a 



' "Zijnde ieder lap gefatzoeneerd als een hand van een kind." (Araboinsche Rariteitkamer, p. 60.) 



