44 



develnpiuoJil it. comes to lie far iu, and its (■ouueclioii 

 Avitli tlie exterior is lost. It is foiuid tiiially just postiMMor 

 to the pleiiro-pedal connective on either side (tig. 2-')). 



The otocysts of the two sides are bound to one another 

 by a fibrons baud passing ventral to the pleuro-})edal 

 couuectives, and just iu front of tlie j)edal ganglia. 

 This band is continued a short distance beyond the 

 otocysts and termiiuxtes in the dorsal surface of the foot. It is 

 probably related to the equilibrating function of the otocysts. 



The otocyst nerve passes ventral to the [)Uni)'o-])(Mhil 

 connective and goes forward between the cerebro-jK'dal 

 and cerebro-pleural couuectives, fusing Avitli the latter 

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

 the cerebral ganglion. The otocyst itself is a cavity lined 

 by ciliated epithelium, the cells of Avhich are in intimate 

 communication with the underlying nerve fibres. The 

 jiiudeus of these cells is more voluminous than in epithelial 

 cells, and in both Patella and Haliotis the cells are smaller 

 and longer than in many other forms. The otoliths are 

 small, usually rounded and numerous ; the otocyst nerve 

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

 distance away from the nrain cavity of the otocyst (lig. 27). 



The Osph'dd'ut are patches of brown-pigmented 

 epithelium, situated at the sides of the posterior part of 

 the nuchal cavity, as already stated. 



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

 and, beneath them, we find a group of multipolar 

 gaiigiidu cells (os])hra(lial ganglion). In tlic 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 liui})et's 

 ancestors. Their lacunse are encumbered with corpuscles, 

 and Boutau iliinl<s tlu^y liave some special glandular 

 functi(Hi connected with the blood. 



