IV. Studies on the development of larval nephridia. Part II.— Polygordius

Abstract
The nephridia of the Polygordius larva have been made the subject of numerous investigations. Among the earlier authors, the work of Schneider (19), Hatschek (8), and Fraipont (6) is the most important, while in recent years the papers of Goodrich (7), Meyer (17), and Woltereck (28 and 29) have made valuable additions to the literature. In the youngest larva figured by Hatschek (8), Fraipont (G), and Meyer (17), the head-kidney is already well formed and functional, and the important work of these investigators deals only with the period of development intervening between the youngest Trochophore stage and the formation of the worm. Of the stages antecedent to this, the pre-larval or pre-trochophoral period, nothing was known when the present work was undertaken. Fraipont (6) had made a few observations on the fertilised egg, while W ilson (26 and 25) had published a few notes and figures on the segmentation. It was important that this early period of development should be investigated, and especially the stages at which the larval excretory organs make their appearance. My main object in undertaking the present work has been, therefore, the investigation of these stages; the first appearance of the larval nephridia, and the origin of their flame-cells or solenocytes . At the time I was unaware that Woltereck (29) was then making a detailed study of the early development and cell-lineage, so the publication of the present paper after his recent contribution necessarily renders it, in part, a confirmation of his results. He has, however, but briefly considered the origin of the nephridia, and the development of the solenocytes has received no attention. Both these points in the present paper I have investigated in more detail.

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