Memoirs: Studies on Earthworms

Journal of Cell Science, Feb 1886

WILLIAM BLAXLAND BENHAM

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Memoirs: Studies on Earthworms

By 0 land Benham, B>Sc, Demonstrator in the Zoological Laboratory of University College , London - Amongst the earliest papers dealing with Earthworms anatomically are those of Savigny (1) in 1820, and of Duges (2) in ] 828, who describe numerous species of Lumbricus, which will be mentioned in Section I I . Duges figures the prostomium of some of these, and describes the genital organs; but his interpretation of the latter is wrong, since he has, like so many of the earlier writers, confused the seminal reservoirs and the spermathecse, attributing each to the wrong sex. Other authors followed him, who, whilst contradicting him, were no nearer the truth. Von Siebold (3), for instance, suggested that the ovary was invaginated into the seminal reservoirs. Even till quite recently the " seminal reservoirs " were spoken of as " testes." I may at once say that I shall use the former name for the three pairs of large white organs in Lumbricus which originate in somites x and xi and spread into the neighbouring somites, and for their homologues in other genera. The ovary was unknown till 1853, when d'Udekem (4) described it in L u m b r i c u s a g r i c o l a j whilst in 1856 Hering (5) supplemented our knowledge of the genital organs by his figure of the ovary and his description of its position on the posterior face of the septum between somites xn and XIII. He also showed that the oviduct was not in continuity with the ovary, but that the ova fell into the body cavity, and were conveyed thence to the exterior by the wide ciliated funnels of the pair of short oviducts which pass through the posterior septum of somite XIII to the exterior in xrv. Hering described the process of copulation, and thought that the spermatozoa passed from the sperm pore along a groove of the ventral surface to the spermathecse; but Dr. Fraisse, in 1882 (6), describes the spermatophores of various spcies of Lumbricus, and shows that the spermatozoa do not pass directly into the spermathecse, but are received in bodies secreted on somite xxvi. Previous authors had described as " testes" the large white sacs which are now known as " seminal reservoirs," but Hering, in this paper, describes and figures the true t e s t e s . Professor A. G. Bourne was the first to figure them in their true position attached to the anterior septum of somites x and xi, as two pairs of small flat appendices. This figure and description occur in a paper by J. E. Blomfield (7), who describes the development of the spermatozoa in the reservoirs. The sperm d u c t s were rightly described by Leo (8) in. 1820, but Duges (2) wrongly considered them as oviducts. The n e p h r i d i a or "segmental organs" also were erroneously interpreted by Dr. Williams in 1858 (40), being considered as respiratory organs. Their true function was first suggested by d'Udekem (9) in his description of Tubifex, whilst Gegenbaur (10) in 1853 published the well-known drawing of this organ of L u m b r i c u s agrieola, the histological structure of which was described by Claparede (11). In regard to the c l a s s i f i c a t i o n of Earthworms, that of Claparede (12) in 1862 is usually followed. He divides the order Oligochseta into two families, Limicolse and T e r r i colffi, but the characters of the latter, as opposed to the former, were derived from the genus L u m b r i c u s only, and now, since the investigation of other genera, no longer hold true. These are his characters: a. The possession of two ventral blood-vessels. b. The presence of nephridia in the same somites with the sperm ducts and oviducts. c. The position of the clitellum far behind the male pores. d. The presence of a vascular network on the nephridia. Now, Perrier's genus P o n t o d r i l u s (13) and Perichseta have no subneural blood-vessel [Microchseta1 resembles these two genera in this respect], and very possibly others will also be found without this vessel. The position of the clitellum is now known to vary; sometimes it is in front, sometimes around as well as behind the male pore. The truly distinctive characters of the Terricolas (or Lumbricinse, as Perrier calls them), as opposed to the Linricolss, are the following: 1 Names or sentences in square brackets refer to results of my own research. a. The presence of nephridia in the same somites with the genital ducts (except in some species of Perichseta and Pleurochseta (Megascolex), where nephridia are unknown in any somite, and in P o n t o d r i l u s , in which the nephridia are said not to commence1 till the hinder region of the sperm duct, so that there are none in the somite carrying the oviduct). b. The abundant vascular network on the nepridia and body wall. c. The almost universal presence of a gizzard (Pontod r i l u s is again an exception). d. The much smaller size of the ova and the compactness of the ovary. But even these charcters may have to be altered as new forms are studied. These Lumbricinas Perrier divides into (...truncated)


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WILLIAM BLAXLAND BENHAM. Memoirs: Studies on Earthworms, Journal of Cell Science, 1886, pp. 213-302, s2-26/102,