36 THE ZOOLOGIST. 
How to Sex Cage Birds (British and Foreign). By A. G. ButiEr, 
Ph.D., &c. ‘The Feathered World” Publishing Office. 
THE opening words in the introduction to this very useful 
volume may be taken as its justification :—‘‘ Amongst technical 
ornithologists it has been a custom, much to be deplored, to 
describe all birds in which the sexes do not exhibit marked diffe- 
rences in colour of plumage, or well-defined external ornamenta- 
tion, as follows: ‘Female similar to male.’’”» In America more 
minute examination is now being made with unsexed preserved 
skins, and keys being sought to discriminate the sex of same. 
This question has for some years engaged the attention of Dr. 
Butler, and it is a study for which he was particularly well 
equipped. Not only is he a well-known aviculturist, and has 
had a large number of live birds both British and foreign under 
his constant observation, but for many years he was in charge 
of the Lepidoptera at the British Museum, where he was recog- 
nized as having acquired a remarkable keenness in the detection 
of minute differences among butterflies and moths. This faculty 
has now placed him in an excellent position for the discrimination 
of the slightest sexual characters in the plumage and superficial 
structure of birds. He has also made prolonged examination 
among the skins contained in the wonderful collection of the 
British Museum, and has compiled sexual descriptions, where 
available, from much of the ornithological literature. The result 
is this small and well-illustrated volume, which will long remain 
a text-book on the subject. In some cases the differential equa- 
tion will not appear so clear to those who have not the trained 
eyes of the author for the lesser distinctions, which are not in- 
frequently difficult to express in words. A shepherd is said to 
individually recognize his sheep—another acquired faculty which 
is difficult to explain in words, and requires personal tuition and 
an apt pupil. Dr. Butler, however, has given us a book which 
clearly sets forth a large number of clearly apprehended sexual 
differences, and as to a considerable number of others he gives 
the key for a more difficult identification. 
This small volume is amply illustrated, and contains four 
coloured plates. 
