720 



ZOOLOGY 



SECT. 



mantle-cavity, where each expands into a large, flat, pallial or 

 stellate ganglion (Fig. 621, l.st. g.) which is visible in front of 

 the ctenidium when the mantle-cavity is opened. From the 

 outer edge of this are given off a number of nerves supplying 

 the various parts of the mantle. 



The organs of special sense of the Cuttle-fish are much more 

 highly developed than those of Triton. The eyes (Fig. 631) are 

 supported by curved plates of cartilage connected with the cranial 

 cartilage. The significance of the various parts of the eye will not 

 be fully understood till the structure of that of the Vertebrata has 



scl.cart 



ci. 



corn 



ir 



scl.cart 



orb.ca.rt 



Ki<;. Ci31. Sepia, section >of eye. oil. proc. ciliary processes; corn, cornea ; ir. iris ; kits, lens ; 

 opt. .'/. optic ganglion ; orl>. cart, orbital cartilage ; rdx. rods ; ri.t. retina ; ./. cart, sclerotic 

 cartilage. (From Vogt and Jung, after Hensen.) 



been studied. A transparent portion of the integument covering the 

 exposed face of the eye is termed the cornea (corn.'). This is perfor- 

 ated by a minute aperture placing the internal cavity of the eye in 

 communication with the exterior. The eye-ball has a firm wall, or 

 sclerotic, strengthened by plates of cartilage (scl.c<~irt.\ Externally, i.e., 

 on the side turned towards the surface of the head, this presents 

 a large opening the pupil. The part of the sclerotic which im- 

 mediately bounds the pupil is termed the iris(ir.}; it contains muscu- 

 lar fibres by whose action the size of the pupil can, to a limited 

 extent, be increased or diminished. Just internal to the iris and 

 projecting slightly through the pupil is the lens a dense glassy- 



