152 GRIFFIN. [You I. 



3.5 mm. in the direction of their long diameter. The end of 

 the auditory nerve spreads out fan-wise upon their surfaces. 

 The auditory nerve has its origin in the cerebral ganglion. 

 In its course it passes over the pedal ganglion, where the 

 sheaths of the nerve and the ganglion are so closely united as 

 to make it appear that the nerve has its origin in the pedal 

 ganglion. 



The otoliths are white calcareous bodies, 2 mm. by i^ mm. 

 by i mm. These dimensions are average. In form, the 

 otoliths are roughly ovate ; though the shape varies to a slight 

 extent, not always being exactly the same in the two otoliths 

 of one Nautilus. Each otolith consists of an immense number 

 of small elliptical crystals, solidly cemented together. The 

 crystals vary in size from .0011 mm. to .0066 mm. in thick- 

 ness, and in length from .0033 mm. to .014 mm. The crystals 

 are composed of calcium carbonate, giving characteristic chemi- 

 cal and light reactions. They all have the shape which would 

 be assumed by a perfect crystal of dog-tooth spar if all the 

 angles were rounded. Very frequently cases of the twinning 

 of two or more crystals are seen. In cases where two crystals 

 are twinned the angle between their axes is usually 78, 

 any divergence from this angle being quite small, so far 

 as observed. In cases of twinning the ends of each crystal 

 are as perfect as in single crystals. These unions of several 

 crystals form the cross and star-shaped bodies, "etc.," men- 

 tioned by Macdonald ('55). The bright points observed by 

 Macdonald are seen only when the focal plane of the lens is 

 above the plane of the crystal. 



Macdonald seems to have been the only one who has dis- 

 sected the otocysts of Nautilus. He dissected a fresh speci- 

 men of Nautilus umbilicatus, and was the first to rightly locate 

 the otocysts of Nautilus. He, however, describes the otocyst 

 as "filled with a cretaceous pulp consisting of minute, ellipti- 

 cal otokonia." As far as regards the " otokonia " I agree per- 

 fectly with Macdonald. But in every case in which I have 

 dissected the otocyst of Nautilus pompilius I have found a 

 single large otolith, and not in any case a cretaceous pulp. 

 When this mass was boiled in concentrated solution of caustic 



