Elementary text-book of zoology. Special part: Mollusca to man / by C. Claus ; translated and edited by Adam Sedgwick ; with the assistance of F.G. Heathcote.

  • Claus, Carl, 1835-1899.
Date:
1897
Catalogue details

Licence: Public Domain Mark

Credit: Elementary text-book of zoology. Special part: Mollusca to man / by C. Claus ; translated and edited by Adam Sedgwick ; with the assistance of F.G. Heathcote. Source: Wellcome Collection.

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    KIS surface of the mantle and on the gills into the mantle and respira- tory chamber. Food materials pass with the water to the labial palps, and so to the mouth. The edges of the mantle lobes do not always remain free through their whole extent, but frequently fuse together, first at the hind end, and then gradually forwards. As a result of this fusion, a posterior opening, including in itself the inhalent and exhalent orifices, becomes separated from the anterior opening into the mantle cavity; and, further, the exhalent and inhalent openings become separated from each other by a transverse bridge of tissue. The long anterior opening or foot-deft, in consequence of the progressive fusion of the mantle edges, often becomes gradually so shortened, that the foot, which is correspondingly reduced, can scarcely be protruded. In this case, the mantle comes to have the form of a saccular investment with two openings. The further forward the fusion of the two mantle lobes proceeds, the more marked becomes a peculiar elonga- tion of the posterior mantle region round the inhalent and exhalent openings—an elongation of such a nature that two contractile tubes, or siphons, become formed (fig. 499, a). The latter may reach such a size that they can no longer be drawn between the posterior edges of the gaping valves of the shell. The two siphons often fuse with one another; but the two canals with their openings surrounded by tentacles, remain separate. In the most extreme cases, the siphons are enormously enlarged, and the posterior region of the body is peculiarly elongated and uncovered by the rudimentary shell; so that the whole animal acquires a vermiform appearance, the shell-bearing anterior region of the body constituting the head (Teredo, fig. 505). The mantle and skin consist of a cellular, slimy epidermis, beneath which lies a connective tissue, richly traversed by muscular fibres. The epidermis on the outer surface of the mantle consists of columnar cells; while on the inner surface of the mantle the cells composing VOL. II. 2 ig. 499.— a, Mactra elliptica, animal with shell; KIS, cloacal or exhalent siphon; KS, branchial or inhalent siphon; P, foot- 6, left valve of M. eolida; VÄT, anterior adductor muscle; JIM, posterior adductor muscle; Ml, pallial line; Mb, pallial indentation.