Memoir: The Study of Nephridia and Genital Ducts Since 1895

Abstract

In 1895 a general review of the morphology of nephridia and genital ducts, and their relation to each other and to the coelom, was published by me (Goodrich, 1895). The present paper is a similar review of the work done since that date on these organs throughout the Metazoa Triploblastica. It is shown that a great many newly discovered facts support the conclusions put forward in 1895, notably the conclusion that two different organs of independent origin--genital ducts and excretory nephridia--can be traced through the various Phyla of Triploblastica. The Gonocoel theory is accepted as the best explanation of the origin of the coelom. In all the various groups coelomoducts, primitively acting as genital ducts, are shown to be derived from the epithelial wall of the gonadial sac, or its derivative the coelomic sac, as centrifugal outgrowths which meet the ectoderm and come to open to the exterior; whereas the excretory nephridia are to be derived from superficial rudiments, often in the form of nephridioblasts, which develop centripetally, and give rise to the whole nephridium whether protonephridial or metanephridial. The nephridial rudiments are not developed from the coelomesoblast, but are either of ectodermal or of ectomesodermal origin. The coelomoducts are always of coelomesoblastic origin. In some Polychaeta (and possibly some Archiannelida) nephridium and coelomoduct may combine to form a nephromixium of both excretory and genital function. In many groups some of the coelomoducts may secondarily acquire an excretory function. In such groups nephridia may disappear, or be no longer developed; provisional larval nephridia may, however, persist until the excretory coelomoducts are developed. Suggestions for the improvement of the nomenclature of these organs and their specialized modifications are made (pp. 117,119). Incidentally many new unpublished observations on their structure and development are recorded. More particularly may be mentioned the early development and morphological relations of the nephridioblast in Tubifex (p. 271).