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XXI.—On a Rule of Proportion observed in the Setæ of certain Naididæ.

Published online by Cambridge University Press:  06 July 2012

J. Stephenson
J. Stephenson
Affiliation:
Professor of Zoology, Government College, Lahore.
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Extract

The common forked setæ which constitute the ventral setal bundles in the Naididæ possess, like the simple setæ of many of the earthworms, a slight swelling on the shaft, the so-called nodulus. The setæ themselves are the principal organs of locomotion, being used as levers, which obtain a hold of the substratum by means of their hooked and forked distal ends; and besides being movable in an anteroposterior direction they are capable of some degree of protrusion and retraction. The position of the nodulus on the shaft is held to regulate the distance to which the seta can be protruded; though it can be retracted so that the nodulus is below the level of the epidermis, it cannot be protruded beyond that degree which brings the nodulus level with the surface.

Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 50 , Issue 4 , 1916 , pp. 783 - 788
Copyright
Copyright © Royal Society of Edinburgh 1916

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References

page 783 note * Cf. Vejdovsky, System und Morphologie der Oligochaeten, 1884:—“Es (the nodulus)ist offenbar eine Regulative für die Hervorstreckung eines bestimmtes Borstentheiles aus dem Leibesschlauche. Der nodulus steckt nämlich beständig in dem Integument, kann auch tief in die Leibeshöhle eingezogen werden, kommt aber niemals, oder nur ausnahmsweise über die Körperoberfläche heraus” (p. 74).

page 783 note † “Studies on the Aquatic Oligochæta of the Punjab,” Rec. Indian Museum, vol. v, pt. i, 1910.

page 784 note * The worm was described as “a species of Dero found in Lahore”; but since the species possessing palps are now separated from those without, it becomes an Aulophorus.

page 784 note † The technical difficulties of observations on the setæ may be overcome by a method which is well explained by Piguet, , “Observations sur les Naïdidées,” Rev. Suisse de Zool., t. xiv, 1906.Google Scholar A living specimen is allowed to remain in water under a cover-glass while the water gradually evaporates; it becomes more and more compressed, and finally, flattening altogether, disintegrates. A small drop of glycerin, placed at the edge of the cover-slip at this stage, before air is sucked in under the cover, will, as evaporation goes further, enter underneath the cover-slip and convert the specimen into a permanent preparation. In successful preparations the setæ, which can now be observed flat and in one plane, are seen laid out in their proper order and disposition in the bundles, as shown in text-figs. 2 and 3 (taken actually from a preparation of Hœmonais laurentii) on p. 772 ant.

page 788 note * The general disposition of the setal bundles in a number of the Enchytræidæ appears to be the same—the points of the setæ being in the same transverse line, and the obliquity of their direction increasing towards the inner side of the bundle, though there is no nodulus (compare figs, of ventral bundles in species of Marionina and Lumbricillus, in a paper by the writer: “On some littoral Oligochæta of the Clyde,” Trans. Roy. Soc. Edin., xlviii, part i, text-figs. 2 and 3).