During a study on the ability of certain synthetic oestrus-producing compounds to induce a sex change in the feather pigmentation of the Brown Leghorn capon (Cook, Dodds, and Greenwood, 1934) it was noted that injections of the same preparation at varying times did not always cause a similar response in the feathers. That such irregular feather responses may be obtained limits the usefulness of the capon test, it was therefore necessary that more should be known of the reaction and an attempt made to determine some, at least, of the factors causing the variation in response. An analysis of our previously collected data on the action of oestrone confirmed the opinion of Lillie and Juhn (1932) that the reactivity of the feathers of test animals varied considerably, but there was no evidence to show whether variable responses to the same stimulus occurred in one and the same individual or, if this were so, whether the changes behaved in a definite manner correlated with a varying environmental factor, such as season for example.
The earliest example of sexual dimorphism in bivalves—evidence from the astartid Nicaniella (Lower Jurassic, southern Germany)
