268 MOLLUSCA. 
mass to the séomach—which is a dilatation of the alimentary 
tube—and is continued onwards as the cztestine. A little 
way up the coil the intestine bends on itself and receives the 
ducts of a four-lobed digestive gland. The fourth lobe 
occupies the top spiral of the shell. After another bend the 
intestine ends in the rectum. 
The nervous system consists of ganglia and connectives, 
but the ganglia are to a large extent concentrated. The 
brain (or cerebral ganglia) lies dorsal to the 
cesophagus* and is joined by two connectives 
on each side to the ventral nerve-mass. ‘This is formed 
of three pairs of partially-fused ganglia, the pedal, pleural 
and visceral. The brain supplies the eyes and otocysts and 
the buccal mass, whilst the ventral nerve-mass 
sends long nerves to all parts of the body. 
In the substance of the ventral nerve-mass is a pair of 
otocysts, supplied, as stated, by nerves from the brain. 
The snail is hermaphrodite and the reproductive organs 
are complex. ‘The genital organ or ovotestis is a small white 
branching organ situated in the spiral lobe of 
the digestive gland. From it the genztal duct 
passes as a coiled white tube down beside the columella. 
Here it swells into a wide common duct, and receives the 
opening of the large aldumen gland. The common duct has 
its internal lumen gradually divided into male (é ) and female 
(?) parts bya septum. Eventually these two diverge as the 
thin vas deferens and the thicker oviduct. The vas deferens, 
after bending on its course, terminates in a large protrusible 
penis. At the base of the penis there is a retractor muscle 
running across to the left side of the body and a long hollow 
tube or flagellum. The oviduct receives the spermathecal 
duct, running backwards beside the common duct to ter- 
minate in the round sfermatheca near the upper end of the 
latter.t The oviduct leads into the vagina. Two branched 
mucus glands then open into this, and it ends at the genital 
pore beside the male opening. Just at the opening lies a 
large muscular organ, the dart-sac, in the lumen of which 
there often is found a calcareous dart. 
Nervous. 
Sensory. 
Reproductive. 
_* Occasionally the buccal mass is withdrawn through the nerve-ring and the 
brain is then found lying in front of the former. 
+ In Helix aspersa the spermathecal duct has a long flagellum. 
