Further examples of Allometric Growth in Spiders

Summary.Measurements of all the limbs, and of their separate joints, have been made on both sexes of the spiders Linyphia triangularis Cl., Linyphia hortensis Sund., Tetragnatha montana E. Sim., and Tetragnatha extensa L. The values of α in Huxley's formula, y=bxδ, have been calculated for the lengths of all the parts, using the root of the sternum area as the standard. In addition, the values of r (the ratio of length to corresponding length in the penultimate instar) have been found and used to give a measure of growth towards the end of the developmental period.The growth‐gradients, showing relative allometry of the limbs, are similar within each genus, but are different as between the genera.Allometry is positive in the cheliceræ of the Linyphiæ, increasing towards their distal ends, but negative in the legs and markedly so in the male palps. The enforced size‐limits of the palpal organs may be a disturbing factor inducing allometry in other limbs.There is little allometry in the limbs of the males of Tetragnatha, but in the cheliceræ of the females it is positive. Growth in these two spiders is very rapid.The extent of growth (as measured by r) and allometry do not necessarily follow one another in the various joints, and would seem to be independent.Allometry is probably of frequent occurrence in spiders, and seems to be emphasized by sexual influence, probably through the agency of hormones.