Drawing, 'Segmental organ of Nais serpentina' by [Thomas] Williams Plate 6, figure 1 showing a pair of segmental organs of the Nais serpentina [Ophidonais serpentina]. Inscribed recto and verso with publication and plate details. Signed in graphite bottom left, 'Williams'. A pencil inscription bottom right reads '(unfinished)'. The manuscript for this paper is wanting. Subject: Marine Biology Published in Philosophical Transactions as part of paper titled 'Researches on the structure and homology of the reproductive organs of the annelids' by Thomas Williams. Received by the Royal Society on 30 December 1856. Read 12 February 1857. [1856]