628 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



ivtr.tis.co'nt. 



-crn. 



P^9-\k-? 



11. Special Sense Organs, 



Otocyst. — The ear sac (Figure 9, ot'cys.) is of an oval outline, its 

 longest diameter being 7.5 micra, and it lies embedded in the dorsal 

 surface of the pedal ganglion. The otokonia are numerous, minute 

 oval bodies not more than 0.6 micron long. 



Olfactory organ. — The rhinophore possesses a large nerve that sends 

 off numerous branches during its passage from the base to the tip of 



the rhinophore. It is difficult to be 

 certain just how the axons of this 

 nerve terminate in the epidermis. 

 The individual branches can be made 

 out at least half way to the surface 

 of the epidermal epithelium, and I am 

 inclined to believe that they simply 

 terminate in free, unmodified fibrils 

 between the epithelial cells. The ol- 

 factory nerve sends a branch into the 

 tentacle and several into the region 

 of the lips. Here, also, the individual 

 fibrils appear to end in a similar 

 manner to those in the rhinophore. 

 It is probable that the general snout 

 region, as well as the rhinophores, 

 interprets olfactory stimuli, as both 

 are innervated by a single nerve aris- 

 ing fi-om the olfactory ganglion. 



Eye (Figure 12). — The eyes, as 

 already stated in connection with the 

 description of the cerebral ganglia, 

 are in close contact with the optic 

 ganglion. Each eye is completely 

 enveloped in a connective-tissue capsule, which contains a greater 

 amount of connective tissue, nuclei, and fibres than is found in similar 

 tissue surrounding the ganglion. At the base of the eye the capsule is 

 easily traced and is seen to be continuous with that surrounding the 

 ganglion. 



Each eye presents, within the cellular capsule, a single layer of 

 cells, which is divisible into an anterior portion, the cornea, and a pos- 

 terior, the retina. These together completely enclose the lens and a 

 cup-shaped mass of pigment. The lens (Figure 12, Ins.) is an oval or 

 pear-shaped body completely filling the pigment cup and projecting 



Figure 12. Eye. crn., cornea; 

 ivlr. tis. co'nt., connective-tissue 

 sheath; Ins., lens; pig., pigment; 

 rtn., retina. Camera lucida, one 

 inch ocular and one-twelfth oil- 

 immersion objective. X 612. 



