Definition of "nervule"

D. reticulata (Blum l.c.) leaves 3-nerved, besides the 2 marginal nervules, ovate-oblong, acuminated, rounded at the base, or somewhat cordate, reticulated beneath and covered with ochraceous dots; panicles terminal; calyx almost quite entire; anthers fixed by the back, furnished with somewhat rhomboid, inappendiculate connectives.

1832, Geoge Don, A General System of Gardening and Botany, volume 2, page 783

A close examination of the wing will always show a partially atrophied disco-cellular, connecting these nervules of the discoidal with either the subcostal or the median nervures, even when one of them has been described as quite free.

1845, Edward Doubleday, “Remarks on the Genus Argynnis”, in Transactions of the Linnean Society, volume 19, page 481

The origin of the first and second median nervules corresponds to that of the two superior subcostal nervules; and the nervule closing the cell unites with the apical portion of the median nervule at a right angle.

1875, S. H. Scudder, “On the Structure and Transformations of Eumæus Atala”, in Memoirs of the Boston Society of Natural History, Volume 2, Part 4, Number 2, page 415

The branches of these compound veins are known as nervules. The median vein always has three nervules. The nervules of the subcostal veins branch up and outward, with from four to five subcostal nervules, toward the costal margin and the apex of the forewing.

2003, W. J. Holland, Cassia B. Farkas (editor), Field Guide to Butterflies, Revised and Updated Edition, page 12