90 LIMAX ARBORUM. 
Diagnosis.—Limax arborum is distinguished from other Limaces by 
its remarkably gelatinous and transparent aspect, due to its great capacity 
for the absorption of water. It is also readily separable from L. maximus, 
with young individuals of which it is sometimes confounded, by the distinct 
lateral banding upon the shield, and by being incapable of uplifting and 
reflecting the anterior part of the mantle in response to irritation. 
INTERNALLY, the animal is distinguished by a horn-shaped flagellum to the 
penis-sheath, and an appendix or cecum to the rectum, features not pos- 
sessed by Limaa maximus, with which it is most liable to be confused. 
Description. —ANIMAL moderately long and slender with a very soft and gela- 
tinous BODY, of a glaucous-grey, but sometimes of a yellow or rufous tint, or even 
entirely black, usually with a paler mid-dorsal line, bordered at each side by an ill- 
defined darker longitudinal band, which gradually attenuates as it approaches the 
slightly-keeled tail; towards the FooT there are indications of a line representative 
of the outer band of the true Limaces; HEAD similar in colour, but eile than the 
rest of the body; Foor distinctly tripartite and white; SHIELD moderately large, 
rounded in front, and somewhat acutely pointed behind, concentrically striate 
around a sub-posterior nucleus, and marked laterally by a black band on each side, 
which bends inwards at the rear, and forms the so-called lyre-shaped marking; mid- 
way there is also often a greyish shade, which gives the aspect of a longitudinally 
trifasciate shield. Length usually about 75 mill., but sometimes much larger. 
Mucus colourless and very iridescent. 
SHELL ovaliform, somewhat wider at the apical end, 
slightly convex, very white, glistening, and iridescent 
above, with the lines of increase close, sharp, and well 
defined, concave and somewhat dull beneath. 
Length, 4 mill.; width, 2% mill. 
The shell of L. arborwm is, however, exceptionally 
variable both in size and substance; examples have been Fic. 106:< tnternal sheten 
recorded 7-8 mill. in length, and the thickness varies Limat arborum, X 5. 
from a delicate plate to an almost cubical calcareous 
mass, which in some cases ruptures the mantle and protrudes through the skin. 
INTERNALLY, the BoDY CAVITY is darkly pigmented, varying from violet to black, 
the colouring being more conspicuous towards the tail, where even the deeper tissues 
are tinged. The fine membrane investing the visceral mass is rich in sooty-black 
pigment cells, but in the anterior part of the body a calcareous netting predominates. 
The NERVOUS SYSTEM shows the buecal and supra- 
cesophageal ganglia to be markedly bilobed ; the sub- 
cesophageal group is apparently formed of four ganglial : ZB 
masses intimately fused together. The dark pigment EG 
which pervades the body cavity of this species gives also 
a lilac tint not only to parts of the brain but even to 
some of the nerve sheaths; the OSPHRADIUM is distin- 
guishable as a broad, flat fissure, with scarcely raised 
puflings, extending towards the left side ; the OTOLITHS *U 
are very numerous, two to three hundred in each cap- ia. 1072 Nerve center 
sule, the prevailing form being oval with a central speck. Limax arborum, X 6. 
The ALIMENTARY CANAL resembles very closely that of L. favus; the SALIVARY 
GLANDS are small, somewhat triangular, and of a yellowish or whitish colour; the 
LIVER varies in colour from a bright golden brown to a dark olive or earthy brown ; 
the KIDNEY is also similar to that of L. flavus, except that it has a very large slime 
gland, which makes broad contact with the head of the ureter; the PULMONARY 
vessels are scarcely raised above the surface of the lung wall. 
The REPRODUCTIVE ORGANS have more affinity with those of Agriolimax agrestis 
than with those of Limax flavus; the OVOTESTIS is in two small roundish dark-brown 
lobes; the DUCT, at first straight and slender, becoming moderately convoluted as it 
approaches the large, yellow, and linguiform ALBUMEN GLAND, the tiny VESICULA 
SEMINALIS being preceded by a conspicuous enlargement; the OVISPERMATODUCT 
is more firmly united than in the preceding species ; the SPERM-DUCT increasing in 
size downwards and abruptly rounded where the channels separate; VAS DEFERENS 
comparatively short, entering a lateral enlargement at end of penis-sheath ; FREE- 
oOvipUCT cylindrical and bluish-white, its lower two-thirds invested with opaque, 
buff-coloured, and plaited glands, which extend to the atrium ; PENIS-SHEATH short 
