Abstract
In 1945 Sproston stated that an alternation of sexual phases takes place in Kuhnia scombri, a monogenean of Scomber scombrus, but an examination of egg-laying, the state of the sexual organs and the presence of sperms in this parasite at various times of the year have shown that there is no evidence for the existence of such a phenomenon. Sproston's observations are examined with particular reference to problems in measuring the length of the parasite and to the unreliability of using the presence or absence of eggs in the uterus as an index of femaleness.