114 DESCRIPTIONS OF PREPARATIONS. 



shaped 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 epi- 

 dermic 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 out- 

 wards between the cells of the epidermis, inwards into the cutis, where they are 

 said by Leydig to become continuous (?) with the pigmented networks there pre- 

 sent. The glands which produce calcareous matter resemble the irregularly-shaped 

 pigment-producing glands, and, like them, open externally and are continuous (?) 



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. Ixxxviii. Abth. i. 1883. For absorption of water in Mollusca, see 

 Schiemenz, Mitth. Zool. Stat. Naples, v. 1884. Cf. Sarasin, C. F. and P. B., ' Directe Communica- 

 tion des Blutes,' &c., Arb. Zool. Zoot. Inst. Wurzburg, viii. pt. i, 1886. 



