8 HOVLE, PterygioteutJiis margaritifera. 



roughly rounded constituent parts of varying sizes. 

 The Hnes of demarcation are more distinct towards 

 the outer surface of the knob. 



(B) The conical projection (c.p.) arises from the front of 

 the spheroidal knob and passes forwards through the 

 aperture at the bottom of the funnel-like inner cone, and 

 spreads out on its inner surface. In structure it is 

 quite similar to the spheroidal portion, except that in 

 many sections its texture seems to be more open, as 

 though it had given way along the lines of division, 

 and there are rather more nuclei than are found 

 there. It seems to be quite distinctly separated from the 

 inner cup. On its anterior aspect this conical projection 

 is hollowed out so as to receive the back of the internal 

 cone (Fig. 3, /. co.). 



The nerves {^Fig. 3 //.) enter the central knob passing 

 through canals which are left between the scales of the 

 posterior cup ; there is more than one nerve twig supply- 

 ing each organ, but I have not been able to trace the exact 

 number, nor to ascertain whether it is constant. The 

 nerve fibre is enclosed in a sheath which is continuous 

 with the connective tissue lying between the scales, and 

 here and there along its course a nucleus is found lying 

 beside it. Externally I have traced the nerve into the 

 fibrous layer, which forms the outer envelope of the organ. 

 In one or two instances I have been able to trace the 

 nerve entering the central mass. It passes directly inwards 

 and gradually disappears, seeming to give off fibres which 

 pass between the cells of which the central mass is com- 

 posed. One or two nuclei seem to be present in the con- 

 tinuation of the nerve fibre. The details of the arrange- 

 ment, however, are not very clear, 



5. The internal cone occupies the cup formed by the 

 hollow prolongation of the central mass and the funnel-like 



