12 
PROFESSOR H. N. MOSELEY. 
Oq thè intermediate or middle shells thè eyes are confined 
to thè arem laterales or to thè liiies of demarcation between 
thè arem laterales and thè area ventralis, which lattei' is usually 
entirely devoid of them. The eyes, which are mostly circular 
in outline as seen on thè shell surfaces, measure about of an 
inch in diameter,in Schizochiton incisus -g-'-,- of an indi, in 
Acanthopleura spiniger and in Corephium aculeatum, 
in which they are ovai in outline, of inch by about 
In Enoplochiton they are smaller stili, and only with 
difficulty seen at all. The eyes appear when viewed by 
reflected light with a simple lens or low power of thè compound 
microscope as highly refracting convex circular spots, looking 
as if made of glass or crystal (see PI. IV, figs. 1, 2, 3, 4). 
The highly refracting spot, thè cornea, is set off by a surrounding 
narrow zone of dark pigment, which is thè margin of thè pig- 
mented eye capsule which forms an iris-like structure round 
thè lens, and which is seen through thè superficial shell 
substance (PI. IV, fig. 3). Through thè centre of each cornea 
is seen a smaller circular area, somewhat darker than thè 
aperture of thè pupil, but showing a brilliant spot of totally 
reflected light due to thè lens. 
Structure of thè Eyes. 
The eyes are evidently to be regarded as having ariseli as 
modifications of megalmsthetes. They are connected with thè 
same network of soft tissues as terminal organs of its ramifica- 
tions in thè same manner, and bave points of resemblance to 
them which are convincing as to thè honiogeny of thè two. 
The soft structures of each eye lie in a more or less pear- 
shaped chamber, excavated in thè substance of thè tegmeutum. 
The stalk of thè pear, which forms thè canal for thè passage of 
thè optic nerve, is directed always towards thè free margin of 
thè tegmentum whence thè nerve reaches it. In Acantho- 
pleura thè eye chambers and thè neural canals continued from 
them follow in direction thè same course as thè megalopores 
and their canals, and join thè main canal ramifications in 
