Dissected so as to show its digestive and reproductive, together with portions of its circulatory and respiratory organs.
The body has been detached from the shell, and the greater part of the mantle and skin has been removed. The coils of the right lobe of the liver (hepato-pancreas), which occupy the upper whorls of the shell and lodge the hermaphrodite gland, are arranged with the rest of the reproductive organs on the right hand: the left lobe of the liver, intestine, heart and respiratory chamber lie to the left: the nerve-collar, buccal mass and stomach occupy the centre. Between the latter and the parts to the left lies at a lower level the sole-shaped 'foot' upon which the animal creeps. A black bristle has been passed between the cerebral or supra-oesophageal ganglia and the buccal mass which contains the crescent-shaped chitinoid jaw and the lingual ribbon or radula, structures invisible here. The buccal mass is somewhat retracted, as it is when the snail 'draws in his head.' On the left side of the buccal mass may be seen the sheath which contains the connectives from the cerebral to the infra-oesophageal ganglia, a small portion of which with numerous nerves proceeding from it is also visible.
From the base of the buccal mass projects the small conical 'sac' of the radula below, while the oesophagus and ducts of the salivary glands enter it above, - the oesophagus between the two salivary ducts. The oesophagus expands into the stomach which is embraced by the salivary glands. The right and left bile ducts, from the right and left lobes of the liver respectively, enter one on either side the pylorus, and at this spot there is a small projecting median caecum. Just below the heart, which has been exposed in the pericardium, and above the aorta cephalica, which has been cut transversely, the intestine passes on to the convex surface of the left lobe of the liver. It reappears on the left side of this lobe in the preparation, on the right side in the natural position of the parts in the living animal, and passes straight to the anus. A white bristle has been placed in the anus through the pulmonary aperture. To the right side of the terminal segment of the intestine is seen the wall of the pulmonary chamber with its network of vessels.
The hermaphrodite gland or ovo-testis is lodged in the concavity of the penultimate and ante-penultimate coils of the right lobe of the liver, which occupy the lowest portion of this preparation on the right hand. From the gland a convoluted hermaphrodite duct passes up to a spleenshaped body, the albuminiparous gland, and from this spot the duct passes upwards again as a much thicker tube consisting of two parts - one, ovi-ducal or uterine, much plicated; the other granulated, the vas deferens. These two parts are not separated completely from one another internally, but at the level of a cylindrical muscular organ, the dart-sac, they become independent. The vas deferens passes to the left, turns round the right upper tentacle, and then passes back again to the base of the penis at the point where the flagellum or organ for secreting the spermatophore also joins it. The retractor muscle of the penis is attached to it near this same point. The flagellum is of great length, and to its right lies a duct of similar, perhaps correlated length, terminated by a bulb. This is the receptaculum seminis or spermatheca, an appendage to the female organs.
Lying below the penis and dart-sac are the two bundles of multifid vesicles, which enter the female duct close to the dart-sac. The generative aperture is on the right side of the head.
The integument varies in thickness in different parts of the body. In the Pulmonata with external shells it is exceedingly thin and delicate where it lines the coils of the shell. It is thicker where it forms the roof of the pulmonary chamber, and thickest of all on the exposed parts of the body. The epidermis consists of a single layer of cells. These cells are columnar and provided with a very delicate cuticula, thickened in certain spots on the tentacles and oral lobes (infra, p. 121-2). The terrestrial differ from the aquatic Pulmonata, and from aquatic Gastropoda in general, in the restricted extent to which cilia are present. In aquatic forms they are as a rule found over the whole of the exposed surface of the body; in the terrestrial Pulmonata, on the contrary, they occur on the sole of the foot but sometimes not over its whole surface; occasionally along its lateral margins (Arion); round the aperture of the supra-pedal gland and that of the pulmonary chamber in some instances (e. g. Helix nemoralis, Limax margin-atus)1. The cells occasionally contain pigment. Among them are scattered on the exposed surface of the body, sensory cells (infra, p. 121), small goblet cells, and the apertures of mucous, pigment, and calcareous, glands.
The mucous glands are unicellular, but project inwards into the cutis. The mucus varies in character, but not infrequently contains whetstone-shaped bodies. The glands are especially large on the collar. Pigment-producing glands are either richly pigmented epidermic cells, e. g. on the collar where they secrete the colouring matter of the shell, or long irregular bodies composed of more than one cell, extending outwards between the cells of the epidermis, inwards into the cutis, where they are said by Leydig to become continuous (?) with the pigmented networks there present. The glands which produce calcareous matter resemble the irregularly-shaped pigment-producing glands, and, like them, open externally and are continuous (?) internally with the cells of the cutis which contain calcareous matter. The pigment and calcareous glands do not extend over the surface of the foot. The latter are especially numerous on the collar, and round the margins of the foot in Helix.
1 Inter-cellular passages are said to exist between the epidermis cells, and are supposed to be the passages by which water enters the blood. They have been described and figured in Helix by Nalepa, SB. Akad. Wien. lxxxviii. Abth. 1. 1883. For absorption of water in Mollusca, see Schiemenz, Mitth. Zool. Stat. Naples, v. 1884. Cf. Sarasin, C. F. and P. B., 'Directe Communication des Blutes,' etc, Arb. Zool. Zoot. Inst. Wurzburg, viii. pt. 1, 1886.