LAWSON, ON LIMAX MAXIMUS. 25 | 
being at the superior and posterior border of this structure ; 
they are of a dumb-bell shape, slightly curved, their concave 
edges embracing the convexity of the head; they are of a 
whitish-yellow colour, but do not contain as muck. calca- 
reous matter as the ganglia of the posterior divisions ; they 
are attached to each other by their posterior expan- 
sions, through the medium of a strong, nervous filament, 
4+ inch in length. From their anterior extremities eight 
nerves pass off, four on each side, to supply the various 
portions of the gustatory and lingue-prehensile apparatus ; 
finally, from each posterior extreme, a minute, lingual twig is 
seen passing to the superior surface of the gullet, and two long 
internuncial branches, which take their course backwards, 
on the upper surface of the cesophagus, for a distance of 
about 2 inch, and terminate in the second circle. This 
is formed of two irregular, oblong pieces (one lying on 
the gullet, and the other beneath it), and a connecting 
nerve, which passes vertically downwards on each side, 
and which, though apparently a single fiattened structure, is 
actually composed of two riband-like nerves, from which 
no branches are given. The upper ganglion-mass is slightly 
concave, both anteriorly and posteriorly, but more so behind 
than in front; it is composed of two ganglia, which have 
become completely amalgamated, and which are indicated 
by a transparent colourless spot at each extreme. That the 
ganglia are not merely contiguous, I have satisfied myself, 
and, from my own repeated observations, must give unquali- 
fied denial to the assertion of Von Siebold,* that the gan- 
glia, though fused into one in Murex and others, are not 
so in Limax. This nerve-mass is easily seen on removing 
the heart, intestine, and reproductive organs, and is the more 
readily perceived on account of its snowy whiteness, which I 
imagine is due to the presence in large quantity of calcareous 
granules, for when the structure has been for some time im- 
mersed in acetic acid the colour is lost, and the mass becomes 
transparent. From the translucent and crescentic ends of 
this supra-cesophageal mass, four pairs of nerves arise; of 
these, the first pair passes to the superior tentacles, supplying 
these organs with filaments, and transmitting a branch to the 
eye, which is the true optic nerve ;+ the second pair is 
also distributed after many divisions to the inferior tentacula 
and lips; the third pair runs downwards and forwards, and, 
* See ‘ Vergleichenden Anatomie,’ Burnet’s translation, note 9, p. 235. 
tT Johannes Miiller (Ann. des Sci. nat.,’ xxii, 1831) maintains this view 
also, which, so far as I can see, is the correct one. It is strange, however, 
that Siebold contends for the distinctness, from its origin, of the optic nerve. 
