90 LIMAX ARBORtJM. 



Diagnosis. — Limax arhorum 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. nmx'mus, 

 with young individuals of which it is sometimes confounded, by the distinct 

 lateral banding upon the shield, and by being incapable of upUfting 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 ccecum to the rectum, features not pos- 

 sessed by Limax maximus, with which it is most liable to be confused. 



Description. — AnimaIj 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- 

 delined 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 paler than the 

 rest of the body; FOOT 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, 2J mill. 



The shell of X. arborum is, however, exceptionally 

 variable both in size and substance ; examples have been pj^ jQg —Internal shell of 



recorded 7-8 mill, in length, and the thickness varies Limax 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 NEKVOUS system shows the buccal and supra- 

 cesophageal ganglia to be markedly bilobed ; the sub- 

 cesophageal group is apparently formed of four ganglial 

 masses intimately fused together. The dark pigment 

 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 

 puffings, extending towards the left side ; the otoliths 

 are very numerous, two to three hundred in each cap- p,^ 107— Nerve centres of 



sule, the prevailing form being oval with a central speck. Limax arborum, x 6. 



The ALIMENTARY CANAL resembles very closely that of L.flavxis; 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 agrestic 

 than with those of Liniax Jlaviis ; 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 yesicula 

 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 wliere the channels separate ; VAS deferens 

 comparatively short, entering a lateral enlargement at end of penis-sheath ; free- 

 OVIDUCT cylindrical and bluish-white, its lower two-thirds invested with opaque, 

 buff-coloured, and plaited glands, which extend to the atrium ; penis-sheath short 



