THE ANATOMY OF PENTASTOMUM TEKETIUSCULUM. 37 



The nerve-cells are very distinctj and do not form a layer of 

 the same thickness all over. They are more numerous at the 

 bases of the nerves where the latter arise from the ganglia 

 (fig. 60), and are more strongly marked ventrally than dorsally 

 (fig. 53) ; a double layer of them passes up along the line which 

 corresponds to the internal faces of the two fused ganglia. The 

 cells are, as a general rule, pear-shaped, with a single branch 

 passing off, and a distinct nucleus and often nucleolus. At 

 times two branches may be given off, and more rarely three. 

 Where the nerves arise (fig. 53) can be seen thin and elon- 

 gate cells pulled out in the direction of the length of the 

 branch, and similar structures (fig. 61) are clearly marked all 

 along the course of the posterior cords, especially in young 

 specimens. 



8. Sense-Or gans. 



As described in connection with the account of the external 

 anatomy, there are present in the female eight and in the male 

 nine pairs of papillse, of which two are much more prominent 

 than the others. These two are the " Tastpapillen " of 

 Leuckart, and on cutting sections are found to contain sense- 

 organs of some nature. 



Of the seven pairs of papillae present in P. proboscideum, 

 Stiles states that only two, those placed immediately above 

 the hooks, contain sense-organs, though the others seem to 

 have nerves running to them. Leuckart^ described at the 

 termination of the special nerve running to the "Tastpapillen" 

 a little swollen mass, containing what he took to be ganglion- 

 cells amongst the nerve-fibres, though he could not with 

 certainty establish the direct connection between the two. 



Stiles- has described and figured a small oval mass of cells, 

 the outer end of the mass projecting beyond the cuticle, and 

 having a small concavity containing a few small stiff" processes. 

 The inner end is connected with a slender nerve. 



In P. teretiusculum there is no difficulty in detecting 



» Loc. cit., p. 25, Taf. ii, fig. 1. 

 ■ Loc. cit., p. U7, Taf. vii, fig. 23. 



