OPPENHEIMER. — RHYNCHOBOLUS DlBRANCHIATUS. 561 



the nerve plexus, that belonging to another cell of the same papilla 

 may liend to the right, as is to be seen in Figures 10 (Pi. 2), 12, 

 and 19 (PI. 3). Occasionally the fibres twist around each other, and 

 there is sometimes to be found an appearance which suggests anas- 

 tomosis of these fibres, but focusing shows that in a great number of 

 such cases the fibres cross without touching each other ; in still other 

 cases (PI. 3, Figs. 12, 19) the blue staining is not confined to the 

 fibres, and this makes the following out of the fibres more difficult. 



The condition shown in Figure 15 (PI. 3), which seems to be an ex- 

 ception to the rule that the basal end of each spindle-shaped cell body 

 tapers into a nerve fibre, is probably the result of the well-known 

 capriciousness of methyleu-blue staining. In no case have I seen a 

 nerve fibre arise from an abruptly rounded basal end of one of these 

 sensory cells, but the cell body seems always to taper gradually into 

 the nerve fibre. There are, however, quite a number of cases in 

 which the inner end of the cell body does not simply taper into a 

 single nerve fibre, but in which it is prolonged into a few processes 

 which ultimately unite to form the fibre (PI. 4, Figs. 23, 25). 



These nerve fibres on their way to the longitudinal nerves often show 

 at intervals those characteristic swellings, or varicosities, which have been 

 so frequently figured in recent works on nerve fibres treated either by 

 the methyleu-blue or the Golgi methods. 



Summary. 



The papillae of the proboscis of Rhynchobolus are sensory organs. 

 They are considered to be sensory on the following grounds : — 



1. The papillae are well differentiated organs. 



2. They are found over almost the entire surface of the everted 

 proboscis. 



3. They are elevated above the surrounding surface. 



4. The cuticula which passes over each papilla is reduced to about 

 two-thirds the thickness it has elsewhere on the proboscis. 



It should be mentioned that the cuticula of the posterior face of each 

 papilla is coarsely corrugated, but the significance of this wrinkling is 

 unknown. 



5. There are two or three spindle-shaped cells in a papilla, each of 

 which terminates — either below the cuticula or more probably at the very 

 apex of the papilla — in what is clearly a sensory structure, and each 

 of these cells tapers gradually at its base into a nerve fibre. These 



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