Chap. XYIII. 
EQUAL TBANSMISSION. 
29T 
or are excited by, tlie ornaments and colours displayed 
before them. There is, however, a striking parallelism 
between mammals and birds in all their secondary sexual 
characters, namely in their weapons for fighting with 
rival males, in their ornamental appendages, and in their 
colours. In both classes, when the male differs from the 
female, the young of both sexes almost always resemble 
each other, and in a large majority of cases resemble the 
adult female. In both classes the male assumes the 
characters proper to his sex shortly before the age for 
reproduction ; if emasculated he either never acquires 
such characters or subsequently loses them. In both 
classes the change of colour is sometimes seasonal, and 
the tints of the naked parts sometimes become more 
vivid during the act of courtship. In both classes the 
male is almost always more vividly or strongly coloured 
than the female, and is ornamented with larger crests 
either of hair or feathers, or other appendages. In a 
few exceptional cases the female in both classes is 
more highly ornamented than the male. With many 
mammals, and at least in the case of one bird, the 
male is more odoriferous than the female. In both 
classes the voice of the male is more powerful than that 
of the female. Considering this parallelism there can be 
little doubt that the same cause, whatever it may be, 
has acted on mammals and birds ; and the result, as far 
as ornamental characters are concerned, may safely be 
attributed, as it appears to me, to the long-continued 
preference of the individuals of one sex for certain in- 
dividuals of the opposite sex, combined with their suc- 
cess in leaving a larger number of offspring to inherit 
their superior attractions. 
Equal transmission of ornamental characters to hoth 
sexes , — AVith many birds, ornaments, which analogy leads 
