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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    municating in part with the other in the mesial line, where they form a kind of indistinct decussation in front of the notch. Distribution of the Cephalic Nerves.—Their roots on each side immediately separate into two trunks, a lower and upper. The former runs above the mouth, to the under side of the first conical segment, or upper lip. Here it divides into several branches, which supply its muscular bands, and then terminate in the integument as a plexus, which appears to communicate wdth that from the first enlargement of the pharyngeal chain, spread over the tubular mouth, which is itself continuous with the upper lip. The upper trunk proceeds directly to the corresponding part of the same segment, and there divides into two branches, of which one in particular, after running the course of the pigmentary laminae, and giving olf a series of short filaments, terminates at the point, beneath the integument. In the pigmentary laminae the nerves form an intricate plexus, and the impression was that many of their ultimate fibres end in loops. They were never seen to be directly connected with the large clear cells scattered through the substance. Nor is there any ground for conjecture with regard to the ofiice of these cells : perhaps they are intended for the transmission of light. From the structure of the segment and the distribution of its nerves, it is not unreasonable to think that its upper surface may be instrumental in the perception of diffused light; and that its under surface and point may be sub- servient not only to the s.ense of touch, but perhaps also to that of smell, in a low degree. That it forms an important organ of search, is pretty evident from the manner in which it is projected alter- nately forwards and from side to side, as the animal advances in its course. The upper side of the cephalic ganglion corresponds to the under side of the subventral, and several points of resemblance are pointed out between the two kinds of centres. Each pharyngeal crus is shown to be a compound structure, composed of different sets of con- necting fibres,—], between its own nerves, which supply, on the one side, the cephalic portion of the outer tube, and on the other, the corresponding part of the alimentary tube reflected inwards from the former ; 2, between these nerves and their fellows of the opposite crus, across the front of the first ganglion ; 3, between the same nerves and the cephalic ganglion; and 4, between the cephal ic