The nervous system of Lumbricus terrestris / by J. Lockhart Clarke.

  • Clarke, J. Lockhart (Jacob Lockhart), 1817-1880.
Date:
[1857]
Catalogue details

Licence: Public Domain Mark

Credit: The nervous system of Lumbricus terrestris / by J. Lockhart Clarke. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    a soft and delicate pad, or upper lip, and is continuous at the sides with the inferior half of the second segment, or under lip, to complete the oral orifice from which the mucous membrane of the mouth is reflected inwards. The mouth is a wide tube surrounded by a deU- cate muscular coat, and attached to the outer tube, or rings, by fine muscular bands. Behind, it dilates into a capacious heart-shaped sac, of which the roof or upper wall is covered by a thick oval mus- cular mass. The outer portion of this mass is divided into distinct, radiating, digital muscles which connect it on all sides and are con- tinuous with the longitudinal muscles of the rings. Its inner surface projects anteriorly into the ca-vity of the pharynx, in the form of a thick circular disc or sucker, surrounded by loose folds of mucous membrane. Opening into the sides of the mouth and pharynx are two or three sets of salivary glands, which consist of convoluted tubules, resembling those of Lepidopterous insects : these glands have not been hitherto detected in Lumbricus ten-estris. The pharynx contracts into a comparatively narrow oesophagus, which in its turn dilates into a capacious crop; and this immediately opens into a cylindrical gizzard composed of a ring of cartilage, with an external muscular coat, and a lining of mucous membrane. A long straight and narrow intestine extends through the rest of the body, and is covered throughout with yellow, follicular, hepatic glands in circles corresponding to the segments. Nervous System.—The central organs of the nervous system con- sist chiefly of a bilobed cephalic ganglion, and a double chain of sub- ventral ganglia extending through the whole length of the body. The lateral lobes of the cephalic ganglion are pyriform, and united by their broader ends in the mesial line. The small end of each divides into two nerve-trunks, of which one forms the root of its cephalic nerves, and the other, the pharyngeal crus, which curves round the side of the pharynx to join the first subventral ganglion. Each crus gives off eight or nine branches. The first four or five arise from the under part of its anterior half, and immediately enter the upper surface of a minute and delicate cord-like chain of ganglia, the enlargements of which correspond to them in number and size. This highly interesting structure lies on the side of the pharynx, con- cealed beneath the crus. The breadth of its first ganghonic enlarge- ment in a good-sized worm, was the of an inch; that of the