14 



(l('vel(i|)iiient if comes to lie iar iu, luid it.s cduiicclioii 

 with the exterior is lost. It is found liually just })osterior 

 to tlie pleuro-pedal eounective on either side (tig. 2-!). 



The otocysts of the two sides are bound to one anotJier 

 by a hbrous band passing ventral to the pleuro-pedal 

 connectives, and just in front of the pedal ganglia. 

 This band is continued a shoit distance bej^jud the 

 otocysthi and terminates in the dorsal surface of the foot. It is 

 probably related to the equilibrating function of the otocysts. 



The otocyst uerve j)asses ventral to the ])leuro-])C(lal 

 connective and goes forward l)etAveen the cerebro-})edal 

 and cerebro-pleural connectives, fusing witli the latter 

 not far from the middle of its length. Its fibres enter 

 the cerel)ral ganglion. The otocyst itself is a cavity lined 

 by ciliated e})ithelium, the cells of which are in intimate 

 communication with the underlying nerve fibres. The 

 nucleus of these cells is more voluminous than in epithelial 

 cells, and in both Patella and llaliotis the cells are snraller 

 and longer than in many other forms. The otoliths are 

 small, usually rounded and numerous ; the otocyst nerve 

 is holhnv, and the otoliths may be found in its cavity some 

 distance aAvay from the main cavity of the otocyst (fig. 'JT). 



The Ospliradui are patches of brown-j)igmented 

 epithelium, situated at the sides of the posterior i)art of 

 the nuchal cavity, as already stated. 



The component cells (fig. 28) are elongated and ciliated, 

 and, beneath them, we find a group of multipolar 

 ganglion cells (osphradial ganglion). In the immediate 

 neighbourhood of the osphradia, and covered by a con- 

 tinuation of this epithelium, are projections, supposed by 

 some to be the last vestiges of the ctenidia of the limpet's 

 ancestors. Their lacunae are encumbered with corpuscles, 

 and lioutan thinks they ]\,\\o some special glandular 

 function connected with the blood. 



