OPPENHEIMER. — RHYNCHOBOLUS DIBRANCHIATUS. 559 



toxylin, I have seen a nucleolus in the basal nucleus only, and here 

 only occasionally (PI. 3, Fig. 16; PI. 4, Fig. 24). Sometimes, 

 though rarely, there are in a basal nucleus two larger granulations 

 (PI. 2, Fig. 11 ; PI. 4, Fig. 30c), which may perhaps be entitled to 

 rank as nucleoli. In preparations stained in iron haematoxylin and 

 in those fixed in vom Rath's mixture the nucleolus is regularly seen 

 with great distinctness near the ceutre of the basal nucleus (PI. 2, 

 Fig. 9b ; PI. 4, Fig. 26-28). The nucleolus is not infrequently sur- 

 rounded by a light area. 



From the different effects produced on the two kinds of nuclei by 

 haematoxylin and by methylen blue, it is fair to conclude that the 

 cells to which the basal nuclei belong are very different from those 

 of the apical nuclei, and that they have nothing to do directly with 

 the nervous system. They are evidently indifferent subcuticular cells, 

 which probably have the same functions as the cover cells of more com- 

 plicated sensory organs. 



The central elongated nuclei found in haematoxylin preparations, 

 judging from their position, evidently correspond to the two or three 

 spindle-shaped cell bodies which appear in methylen-blue preparations. 



" I have not succeeded," says Pollers (p. 690), " in finding proof posi- 

 tive that there are nerves in the fibrous tissue which enters the papilla 

 from the common subcuticular layer." What Ehlers was unable to 

 find, I have, by the use of improved histological methods, succeeded 

 in demonstrating with entirely satisfactory clearness. The spindle- 

 shaped cells are evidently nerve cells of sensory function. For, on 

 the one hand, the basal end is connected with one of the eighteen longi- 

 tudinal nerves of the proboscis by a nerve fibre passing to that nerve, 

 either directly or, through the intervention of the peripheral nerve plexus, 

 indirectly; and on the other hand the peripheral end tapers toward 

 the apex of the papilla, where it terminates in a sensory structure, the 

 precise nature of which it is difficult to make out. 



Each of the sensory cells of the papilla has the form of an elongated 

 spindle tapering at its free end to a delicate fibre-like structure, and 

 continuous at its basal end with a fibre traceable to a nerve trunk. 

 This spindle-shaped enlargement, or cell body, lies in the axis of the 

 papilla and about midway between its base and apex. An exception 

 to this rule regarding the position of the cell body is seen in Figure 20 

 (PI. 3), where the cell seems to have a basal position. I am, how- 

 ever, in doubt as to whether the sensory cells in this case are actually 

 basal in position, or whether the appearance may not be due to an 



