Existing Theories not Satisfactory 
exercise has caused the development and _in- 
heritance of plumes in some species, why not 
in the others? 
Again, Cunningham is not correct in saying 
that sexual dimorphism is “virtually absent” in 
the Columbidz. Few birds display so striking a 
sexual dimorphism as the Orange Dove (Chryseena 
vector) of Fiji, in which the male is bright orange 
and the hen green. We have already cited the 
case of the curious sexually dimorphic red turtle- 
dove. Now, the courting attitudes and actions 
of this species are precisely the same as those of 
other allied turtle-doves; why, then, have these 
exercises caused only one species to become 
sexually dimorphic ? 
Our survey of the more important attempts 
which have been made to explain the phenomena 
of sexual dimorphism leads to the conclusion that 
these still require elucidation. We have weighed 
each theory in the balance and found it wanting. 
The outstanding feature of sexual dissimilarity 
is the apparently haphazard manner of its occur- 
rence. 
We have already alluded to the case of the 
doves in India. In that country four species are 
widely distributed—namely, the Spotted Dove 
(Turtur suratenszs), the Ring or Collared Dove 
(Turtur risorius), the Little Brown Dove ( Zurtur 
cambayensis),and the Red Turtle-dove(Ginopopetia 
333 
