During the detailed study of the finer anatomical structure of the potato tuber nematode, Ditylenchus destructor Thome, 1945, the presence of an apparently hitherto unrecorded structure was revealed. It is situated on the ventral surface of the body just anterior to the excretory pore. It is quite easily seen in living nematodes and has no doubt, in the past, been confused with the excretory pore. It appears as a bright lens-like structure, more highly refractive than the neighbouring parts, especially when specimens are viewed in an approximately lateral position. The structure is really band-like, usually more or less biconvex in section, situated between the cuticle and hypodermal layer.