In the ducts are found columnar cells, sometimes ciliated, but not in H. pomatia (Barfurth), as well as mucous-cells: in the acini three kinds of cells - liver-cells (Barfurth) or granular-cells (Frenzel); ferment-cells (Barfurth), club-cells, or club-shaped ferment-cells (Frenzel); and calcareous-cells. The granular cells contain each a vesicle which incloses a number of more or less coloured highly refractile granules, fat globules variable in size, and albuminous bodies. In Helix the granules are clear yellow in colour; sometimes as in Arion, they are the only coloured constituent of the cells. These granular cells are absent in Cephalopoda. The ferment-cells vary in appearance in different Mollusca. They are absent in Chiton, Patella, Fissurella, and Pteropoda; doubtfully present in some azygobranchiate Gastropoda and some Lamellibranchiata. In shape they are like a club or pear, with the larger end turned towards the cavity of the acinus. They contain each a vesicle inclosing more or less coloured fluid, viscous or semi-solid bodies, fat and albumen globules.
The refractile index of the contents of the vesicle is low in Helix and Cephalopoda, and their colour is similar to that of the granule-cells. It is generally more or less different in the Opisthobranchia and Azygobranchia. It is similar in intensity in Pulmonata, more intense in other groups (Frenzel). The calcareous cells are wanting in Lamellibranchiata, Pteropoda, and in Natantia (=Heteropodd) among Gastropoda, and other isolated instances in this Class. Their size is great, and they are more or less triangular with the base external, and the apex not reaching the cavity of the acini. They contain the so-called calcareous globules, which vary in chemical characters. Lime is always an ingredient, and, according to Barfurth, in combination with phosphoric acid, a view opposed by Frenzel. Barfurth has shown that the percentage of inorganic ash obtainable from the liver of Helix pomatia varies at different seasons. In May the amount averaged 20.24 per cent; in September 25.72 per cent; after the breaking and repair of the shell it fell at once to 16.99 per cent.; and after the formation of the epiphragma to 10.26 per cent, the normal figure during the winter rest of the animal.
It may be added that the quantity of phosphates in the epiphragma is 5.52 per cent, as opposed to 0.85 per cent. in the shell. The mucus of Helix contains lime, and to a very large amount in Arion. The secretion of the liver is acid, and has been found to have a diastatic and a peptic action in H. pomatia. It contains enterochlorophyl in Helix pomatia, in many other Gastropoda, some Lamellibranchiata, and haematin in various Pulmonata, e. g. Helix pomatia, H. aspersa, and Arion ater, etc. Glycogen is found in the liver; in Helix, in the plasma-cells of the connective tissue which are abundant; in Limax, in the liver-cells, the connective tissue being scanty. For the distribution and mode of occurrence of glycogen in the other tissues of Gastropoda, as well as in the tissues of other animals, the very valuable paper of Barfurth's, A. M. A. xxv. 1885, should be consulted.
1 The character of the dentition is especially useful for classificatory purposes in the Azygo-branchiate Gastropoda. The names in use are chiefly the following. The formulae indicate the presence or absence of median, admedian, and in Rhipidoglossa of lateral teeth. Rachiglossa, o. I. o, e.g. Volutidae: Hamiglossa, I. i. i, e.g. Murex, Buccinum: Toxoglossa, I. o. I, e.g. Conidae: Taenioglossa, 3.1. 3, e. g. Cerithium, Natica, Littorina, Paludina: Cteno- or Pteno-glossa, ∞. o.∞, e. g. Ianthina: Rhipidoglossa, 00. 4-7. 1.4-7. ∞, e. g. Turbo, Nerita (also Haliotis, Fissurella, among Zygobranchiata). There are forms of dentition which do not fall under any of the above-written terms, e.g. Patella Vulgata, the Limpet, with 3. 1. 4.1. 3.
The hermaphrodite gland or ovo-testis consists of a number of cylindrical follicles opening into a common duct. The ducts from the various groups of follicles unite in their turn with the chief duct of the gland, which is lined by a non-ciliated squamous or columnar epithelium. The ova and spermatozoa are formed from the lining epithelium of the follicles, but at a different time. The albumen gland is a racemose gland. It opens by a common duct, which with its branches is lined by a ciliated epithelium. The ovi-spermi-duct is lined by a ciliated epithelium, and both portions are beset with glands. The free portion of the oviduct is also ciliated, but not the vas deferens, as is the case also with the penis and flagellum. The latter organ, with the hinder part of the penis, secretes the 'capreolus,' or spermatophore, a structure formed of hardened mucus. It is more or less elongated and its edges folded so as to form a groove in which a mass of spermatozoa are lodged. In copulation it is transferred to the duct of the receptaculum seminis, and in this species it is said to undergo resolution in ten days after transference. The dart-sac, which has extremely muscular walls, contains a pointed cuticular style, with much calcareous matter in its composition.
Its use appears to be a preliminary excitant to copulation, after which act it has been found within the body. A new dart is speedily formed after the loss of the old one. The multifid vesicles secrete a highly refractile fluid, which is poured out during copulation, and is formed by the epithelium. The duct of the receptaculum seminis has occasionally a tubular diverticulum appended to it. The latter is constantly present in many species of the genus Helix, e. g. H. aspersa, and may possess a terminal bulb like the receptaculum itself. The genital organs are richly supplied with nerves and bloodvessels. In aquatic Pulmonata the male and female apertures open separately from one another externally.
Of the accessory organs present in Helix pomatia, the flagellum is absent in all the American species of the genus, and both dart-sac and multifid vesicles, common in the European species, are rare in them. A dart-sac is found in the American slug Tebennophorus; and glands resembling the multifid vesicles are appended to the male organs in Veronicella. With these two exceptions the organs in question are confined to the genus Helix.
The eggs have, like those of other Helices, of Arion and some other terrestrial Pulmonata, a hard calcareous shell inclosing a quantity of albumen and a small ovum. Those of some terrestrial (Limax), and of all aquatic Pulmonata, are devoid of a calcareous shell, and the surface of the albumen is simply hardened. The eggs of H. pomatia are large, nearly a quarter of an inch in size, and are laid in earth as are those of other terrestrial Pulmonata, in masses, but not united, as are those of many species of Limax and of all aquatic Pulmonata. A few terrestrial Pulmonata are viviparous (certain species of Clausilia and Pupa, Helix rupestris, Achatinella, a Vitrina). The larva has but slight traces of the typical Molluscan velum; in that point differing from its aquatic congeners, where it is well developed, and Arion and Limax, where it is wanting. There is no operculum. A remarkable contractile pedal sinus is present. A paired provisional tubular renal organ appears to be found in the larva of all Pulmonata.
Integument.Leydig, A. N. 42, 1876. Epithelium. Flemming, A. M. A. vi. 1870. Connective tissue (interstitial), Brock, Z. W. Z. xxxix. 1883.
Odontophore.Mechanism. Geddes, Tr. Z. S. x. Radula, Rossler, Z. W. Z. xli. 1885. Description of various forms of dentition and nomenclature, Gray. P. Z. S. 1853; A. N. H. (2), xii. 1853; Troschel, Das Gebiss der Schnecken, Berlin, i. 1856-63; ii. parts i-vi. 1866-79. Myohaematin in odontophore muscles, MacMunn, Proc. Physiol. Soc. in Journal of Physiology, v. 1884; P. R. S. xxxix. Novr. 1885.
Salivary glands, etc, see Nalepa (op. cit. ante, p. 112). Sugar formation. Bonardi, Boll. Sc. Pavia, Anno 5,1883. Liver Barfurth, A.M. A. xxii. 1883; Id. Biol. Centralbl. iii. 1883-84; Frenzel, Biol. Centralbl. tom, cit.; Id. A. M. A. xxv. 1885; its physiological action, Krukenberg, Untersuchungen Physiol. Inst. Heidelberg, ii. 1882, pp. 4 and 13; Fredericq, Bull. de l'Acad. Royale de Belgique (2), 46, 1878. Pigments. MacMunn, P. R. S. xxxv. 1883, and xxxviii. 1884-85; Krukenberg, Ver-gleich. Physiol. Studien, ii. (2) p. 63, 1882. Glycogen, Barfurth, A. M. A. xxv. 1885.
Genital organs, Baudelot, A. Sc. N. (4) xix. 1863. Histology of accessory organs, Batelli, Atti Soc. Toscana Sc. Nat. (Mem.), iv. 1880; cf. Journal Royal Micr. Soc.
(2) i. 1881, p. 435. Development, Rouzaud. C. R. 96, 1883; Jourdain, Revue Sc. Nat. Paris and Montpellier, viii. Physiology, Dubrueil, Revue des Sci. Nat., Paris and Montpellier, i. 1873; ii. 1874; cf. Jourdain in A. N. H. (4) viii. 1871. Dart of British Helicidae, Ashford, Journal of Conchology, iv. 1883.
Sperm. Leydig, Untersuchungen zur Anat. und Histol. der Thiere, Bonn, x. 1883, p. 118; development of, Blomfield, Q. J. M. xxi. 1881 j Nussbaum, A. M. A. xxiii. 1884, p. 206; cf. Von Brunn, ibid. p. 459; Platner, A. M. A. xxv. 1885. Ova and Development. Fol, A. Z. Expt. viii. 1880.