Penial and Genital Setæ of Lumbricus Terrestris, L., Müll

Abstract

ON p. 172 of Prof. O'Donoghue's “An Introduction to Zoology for Medical Students,” reviewed in NATURE of August 11, it is stated that in Lumbricus herculeus (the name is a synonym of L. terrestris) “in the fifteenth segment the two pairs of ventral setæ lying close to the male external aperture are modified to form the penial setæ.” In Bourne's “An Introduction to the Study of the Comparative Anatomy of Animals,” vol. 2, pp. 19–20 of the fifth edition, 1912, it is said that in the same worm “the chætæ of the clitellar region differ from those of the rest of the body, being finer and nearly straight, with hooked inner ends. There is also a pair of modified chætæ in somite 15.” Borradaile, in “A Manual of Elementary Zoology,” p. 217 of the third edition, 1920, says, “The ventral setæ of the clitellum, of the 26th and of the 10th to the 15th segments are straighter and more slender than those of other segments, which are stout and somewhat hooked. The modification is in connection with the use of the setæ of the 26th segment during coition, and of the other straight setæ during the formation of the cocoon in which the eggs are laid.” Parker and Haswell, in “A Textbook of Zoology,” p. 455 of the second edition, 1910, state that “the setæ in the clitellum, and those in the neighbourhood of the genital apertures, are much slenderer than the rest.”