PRESENCE OE EYES IN SHELLS OF CERTAIN CHITONI!)^. 7 
diflPereQce between thè two iu size being considerablè. and 
tbere being no pores of intermediate size between thè two. 
The mouth of each megalopore leads into a cylindrical 
chamber hollowed out in thè thickness of thè tegmentum, per- 
pendicular to its surface and more or less dilated iu accord- 
ance with thè form of thè papilliform body contained within 
it. This cylindrical chamber is continued below into a wide 
canalj which in its course towards thè piane of junction of thè 
tegmentum with thè articulamentum is curved towards thè 
girdle margin of thè tegmentum (PI. VI, fig. 6^ pfì). On 
reaching thè piane of junction it joins a plexus of wide main 
canals which ramify horizontally in tliis piane, parallel with 
thè surface of thè tegmentum. 
From thè sides of thè megalopore chambers are given off 
fine canals, which perforate thè tegmentum in a direction ver- 
tical to its surface, and join thè bases of thè micropore cavities. 
In some species a considerable proportion of thè micropore 
canals are also given off direct from thè mairi vertical branches 
of thè horizontal plexus, as in Corephium aculeatum (see 
PI. V, fig. 8). Those springing from thè megalopores may be 
given off from each macropore chamber at thè same, or nearly 
thè same, height all round, or at very various heights (see PJ. 
IV, fig. 10, hh). 
The tegmentum when decalcified persists as a homogeueous 
apparently horny substance, which in some species shovvs a 
finely fibrous structure (PI. VI, fig. 4), but in others appears 
almost structureless. This substance, which is in thè recent 
state of thè shell impregnated with thè lime salts, is termed by 
Vliddendorf thè stroma, and by Marshall, Reincke and Van 
Bemmelen thè cuticula. It retains in thè decalcified condi- 
tion both thè form and dimensions of thè tegmentum itself, 
and thus in sections of thè decalcified shell thè disposition of 
thè contained soft structures with regard to thè hard parts is 
clearly displayed. 
The plexus of horizontal main canals is occupied in thè 
horny shell by a corresponding ramification of strings of soft 
tissue, which are offsets of thè raantle substance, These 
