CHARACTERS OF SPECIES. raid 
sound distinctions for species, or at most— among 
insects — for permanent or sexual differences. We re- 
collect no instances among wild animals, in which these 
marks are known to vary: no better or more tangible 
character, indeed, can be named, than the relative shape 
of the wings of birds, in cases where the size and colour 
of two or more species are perfectly the same. A striking 
instance of this may be seen in the greenlets (Vireo V.) 
of America; where the different shape of the wings con- 
stitutes the only specific distinction of three, if not of 
four, species.* The possession of horns, protuberances, 
enlargements, &c. are mostly characters of types, but 
their particular shape is a sure indication of species. 
When, however, the shape and direction are the same, 
but there is merely a difference of size or developement, 
such circumstance cannot constitute a species. Let us 
look, for examples of this, to the hornbills (Bucerid@) 
among birds; the Scarahbe@ide and the Cerambycide 
among insects, and the Muricide among shells. The 
young hornbills have seldom any of those protuberances 
on their bill, which they acquire with maturity; and 
even then they increase in size, without altering much 
in form, unto advanced age : from ignorance of this fact, 
former writers were very apt to describe the young 
and the adult bird as two different species. An analo- 
gous case to this is met with among the saprophagous 
beetles (particularly in the group of bulky Dynastide 
MacL., and in the genus Phenius of the same author) : 
the hornlike protuberances, which, in the last, distin- 
guishes the male sex, vary, in their length, in almost 
every individual ; so that in some they are very promi- 
nent, while in others they are merely like short tubercles. 
It would be curious to ascertain whether this difference 
results likewise from age. The spines upon the different 
rock shells (Murex), and on the coronated volutes 
(Cymbiola Sw.), vary in like manner ; some specimens 
having acute and prominent spines, while others are 
nearly smooth. These are the most remarkable excep- 
* See Northern Zoology. 
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