INTRODUCTION. xiii 
But the variation does not end here; for in such species as possess freckled coverts, the 
freckles become finer as the bird becomes older ; and in those in which the coverts are 
black, the black becomes purer and more dense. In the case of Pharomacrus mocinno 
the young males in their first plumage are only distinguishable from the females by their 
more pointed rectrices ; but after they assume the normal colour of the adult bird, the 
longer they live the longer and wider the tail-coverts become, the more prolonged the 
wing-coverts, and the more elevated the crest. 
In the ‘ Comptes Rendus’ for 1857 (vol. xlv. p. 688), Professor Bogdanoff gave an 
account of some chemical experiments which he made with the plumes of Pharomacrus 
auriceps, and showed that by immersing the red breast-plumes in spirit all the colour 
is taken out of them. The red pigment of these feathers he calls “zooxanthine.” We 
remember that M. Jules Yerreaux has also stated that in heavv storms of rain, the red 
breast of Hapaloderma narina at the Cape becomes completely washed out, and is renewed 
again in its full intensity only after an interval of some days. A similar fact is noticed 
in the red wing-feathers of the Touracous and in some of the American Chatterers (Cotinga). 
In the fourth part of the ‘ Museum Heineanum,’ Messrs. Cabanis and Heine introduce 
a number of new generic names into this family of birds. The value of these genera 
is very small. Thus we find Pothinus used for a group of yellow-breasted Trogons including 
T. aurantiiventris, a species perhaps not properly separable from T. puella, which is left 
in true Trogon. The rest of the yellow-breasted Trogons are placed in a genus Aganus • 
whilst for T. surucura another generic name, Hapalophorus, is proposed, the species being 
in fact most nearly allied to T. aurantius. For the black-tailed Trogons the generic name 
Troctes is proposed, and with more reason than in the other instances; but here a sub¬ 
division seems hardly admissible, seeing that an intermediate species exists in T. clathratus, 
which partly closes the gap between Trogon and Troctes. Lastly, the genus Pharomacrus 
is divided into two, Tanypeplus and Pharomacrus ; but this, again, seems to me to be carrying 
generic subdivision too far. 
The species described as Trogon neoxenus and placed, in the first part of this edition 
of the ‘ Trogonidse,’ under the new generic name Euptilotis, is also considered by Messrs. 
