162 
Tofitrs. 
parative. In Todus platycircus their length is the 
greatest ; while in viridis and megacephalm they 
are shorter than in melanocephalus. These varia- 
tions are accompanied by differences in the formation 
of the claws and toes ; so that without a competent 
knowledge of the group as a whole, “ good genera," 
as such artificial divisions are sometimes called, 
might actually be made out of several of the species, 
to the no small confusion of all that is true in 
nature or useful in science. It has entirely origi- 
nated, in fact, from such limited views, that the 
Todus viridis has been pronounced “ the unique 
example of its genus and all the other species 
detached from it, and thrown into the common 
receptacle of flat-bellied birds, — “ the great genus” 
Muscicapa. It is needless, however, to criticise 
artificial systems; and therefore let us now see 
what results will be obtained by arranging the 
species above named, and comparing them with 
the types they represent. 
