THE EVIDENCE OF THE AUDITORY APPARATUS 373 



is the cause of the ill-defined appearance of the central pore, just 

 as the terminal pore is much less conspicuous on surface-view in the 

 spike-organs of the flabellurn than in the purely poriferous organs, 

 no part of which projects beyond the level of the chitinous surface. 



The fine tubule is soon lost in the thickened but soft modification 

 of the chitinous layer (ch.) which is characteristic of the sense-organ ; 

 at all events, I have not succeeded in tracing it through this layer 

 with any more success than in the corresponding case of the tubules 



B c 



Fig. 152.— A, Section through Tooth of Pecten of Scorpion; B, Surface View 

 of Sense-Organs ; C, Goblet of Sense-Organ more highly magnified. 



bl. and n., region of blood-spaces and nerves; gl., ganglion-cell layer; ch., modified 



chitinous layer ; 5.0., sense-organ. 



belonging to the smaller goblets of the branchial sense-organ of 

 Limulus already described. 



At the base of the modified chitinous layer a series of cells is 

 seen, many, if not all, of which belong to the chitinogenous layer. 

 Xext to these is the marked layer of ganglion-cells (gl.), similar to 

 those seen in the flabellurn of Limulus. The rest of the space in the 

 section of the tooth is filled up with nerves (n.) and blood-spaces (bl.) 

 just as in the section, Fig. 146, of the flabellurn of Limulus. 



Gaubert does not appear to have seen the goblets at all clearly ; 



