28 The Shell-Collector's Handbook. 
cesophageal ganglia of the snail, and are united by a 
commissure which runs in the middle line over the 
mouth. From these ganglia two connectives arise, 
the cerebro-pedal connectives, which unite the cerebral 
ganglia with another pair of ganglia which are orange- 
coloured, and situated in the foot, known as the 
pedal ganglia. 
From the cerebral ganglia also proceed another pair 
of connectives—the cerebro-osphradial connectives—to 
the osphradial or parieto-splanchnic ganglia, which are 
placed under the posterior adductor muscle, giving 
branches to the mantle and to the substance of this 
muscle. The pedal ganglia give branches to the foot 
and the auditory organs. 
THe AvupiTory Orcan.—The auditory organ or 
otocyst consists of a small rounded or oval sac filled 
with fluid, and containing a central otolith. The 
auditory nerve is a branch of the pedal ganglion. 
THE OspHRADIUM.—An organ in close relation with 
the osphradial ganglion, and which consists of a layer 
of elongated epithelium, has been called the osphradiwm 
by Lankester, and is believed to be olfactory in 
function. 
THE RepropuctiveE Oreans.—Unlike the Gastero- 
pods the Lamellibranchs are dicecious. The generative 
glands are macroscopically alike in both sexes, 
and it is only on a microscopical examination that the 
testis may be distinguished, by its spermatozoa, from 
the ovary, with its ova. They are racemose in 
character, and occupy a large portion of the upper 
part of the foot. Their contents escape into the 
surrounding water through the genital aperture which 
