THE EVIDENCE OF TIlE AUDITORY APPARATUS 365. 
readily than a blood-coagulum, yet in the sense of being structure- 
less it resembles a coagulum, 
The enormous number of these organs crowded together over 
the whole flat surface of the flabellum produces a very striking 
appearance when viewed on the surface. Such a view presents an 
appearance resembling that of the surface-view of the branchial sense- 
organs; in both cases the surface is covered with a great number 
of closely set circular plaques, in the centre of each of which is seen 
a well-marked pore. The circular plaques in the case of the flabellum 
are much smaller than those of the branchial sense-organs, and 
clearly are not protrusible as in the latter organs, the appearance as 
of a plaque being due to the ring of thickly-set canaliculi round the 
central tubule, as already described. When stained with methylene 
blue, the surface view of the flabellum under a low power presents 
an appearance of innumerable circular blue masses, from each of 
which springs a fine bent hair, terminating in a pore at the surface. 
The blue masses are the homogeneous substance (cap.) of the bulgings 
seen through the transparent external layer of chitin, and the hairs 
are the terminal part of the chitinous tubules. Patten has repre- 
sented their appearance in the mandibles in his Fig. 2, Plate I. 
The large tubes in the chitin alter in shape according to their 
position. Those in the middle of the sensory surface of the flabellum, 
in their course through the chitinous layers, are hardly bent at all; 
as they approach the two lateral edges of this surface, their long thin 
neck becomes bent more and more, the bending always being directed 
towards the middle of the surface (see Fig. 146); in this way the 
chitinous tubules increase more or less regularly in length from 
the centre of the organ to the periphery. The large basal part of 
the conical tube contains, besides the chitinous tubule, a number 
of nuclei which are confined to this part of the tube; some of these 
nuclei look like those belonging to nerve-fibres, others are apparently 
the nuclei of the chitinogenous membrane lining the tube. I have 
never seen any sign of nerve-cells in the tube itself. 
The only other kind of sense-organ I have found in connection 
with these sense-organs are a few spike-like projections, the appear- 
ance of which is given in Fig. 149. I have always seen these in the 
position given in Fig. 146 (sp.), ve. at the junction of the surface 
which contains the sense-organs and the surface which is free from 
them. They are, so far as I have seen, not very numerous; I have 
