422 
SEXUAL SELECTION. 
Part II. 
by the males. But from the circumstance of colour 
being so variable, and from its having been so often 
modified for the sake of protection, it is extremely 
difficult to decide in how large a proportion of cases 
sexual selection has come into play. This is more 
especially difficult in those Orders, such as the Orthop- 
tera, Hymenoptera, and Coleoptera, in which the two 
sexes rarely ditfer much in colour ; for w r e are thus cut 
off from our best evidence of some relation between the 
reproduction of the species and colour. With the 
Coleoptera, however, as before remarked, it is in the 
great lamellicorn group, placed by some authors at 
the head of the Order, and in which we sometimes 
see a mutual attachment between the sexes, that we 
find the males of some species possessing weapons for 
sexual strife, others furnished with wonderful horns, 
many with stridulatiug organs, and others ornamented 
with splendid metallic tints. Hence it seems probable 
that all these characters have been trained through 
O O 
the same means, namely sexual selection. 
When we treat of Birds, we shall see that they pre- 
sent in their secondary sexual characters the closest 
analogy with insects. Thus, many male birds are 
highly pugnacious, and some are furnished with special 
weapons for fighting with their rivals. They possess 
organs which are used during the breeding-season for 
producing vocal and instrumental music. They are 
frequently ornamented with combs, horns, wattles and 
plumes of the most diversified kinds, and are decorated 
with beautiful colours, all evidently for the sake of dis- 
play. We shall find that, as with insects, both sexes, 
in certain groups, are equally beautiful, and are equally 
provided with ornaments which are usually confined to 
the male sex. In other groups both sexes are equally 
plain-coloured and unornamented. Lastly, in some few 
