Secondary Sexual Characters 431 
Differences exist not only in color and ornamentation, but in 
other characters also. The male gorilla has a powerful voice, 
the effect of which is enhanced by the presence of a laryngeal sac. 
One kind of gibbon can produce a correct octave of musical notes. 
The vocal organs of the monkey Mycetes are a third larger than 
those of the female and produce an ‘“‘overwhelming” sound. 
In birds also it is generally the male that sings; and in the case 
of the thrushes and several other groups the voice of the male 
is highly developed. 
The scent glands or odoriferous glands of some of the mam- 
mals are also secondary sexual characters. In many cases the 
glands are present and equally developed in both sexes, but in 
others the glands become enlarged in the male during the breed- 
ing season, while in still other species the glands are more 
developed in the males or even confined to them. At the rut- 
ting season the glands on the sides of the face of the male ele- 
phant emit a secretion that has a muskyodor. The males of 
some of the bats have glands and protrudable sacs in various 
parts of the body. The strong odor of the male goat and of 
certain deer is well known. In the male of the musk deer 
there is a region of the tail that is ‘‘bedewed with an odorif- 
erous fluid,” while in the female this space is covered with 
hair. 
The dances accompanying courtship in certain male birds, 
and the peculiar antics and apparent displays of plumage 
shown by these, belong also in the class of secondary sexual 
differences. 
In the group of lizards, amphibians, and fishes, numerous 
cases of secondary sexual differences are known, and in some 
of these the differences are almost as marked as in the highest 
members of the vertebrates. 
In the insects many species show secondary sexual dif- 
ferences. In the flies of the genus Elaphomia the males are 
furnished with horns, recalling those of the stag. They are 
branched or palmated, and in one species are of a beautiful 
pink color edged with black. In the butterflies there are many 
