£4 
PAPILIO. 
natural ; and if it rvere broken up by attaching un- 
due importance to very subordinate characters, no 
partial change would suffice; for any principle that 
might be thought to justify the establishment of 
one genus, would render it necessary, if consistently 
acted upon, to create not fewer than thirty or forty. 
One of the most obvious differences among the spe- 
cies is the presence or absence of a tail ; but an 
arrangement founded on this circumstance, sepa- 
rates, by a wide interval, kinds which are in other 
respects most closely allied. Nay, the tail itself is 
often more or less developed in the same species, 
being sometimes distinct in the one sex while it is 
inconspicuous or wanting in the other ; its value as 
a diagnosis of genera is thus in a great measure de- 
stroyed. 
Considerable differences likewise prevail in the 
appearance of the caterpillars, but these are too im- 
perfectly known to be made the groundwork of an 
arrangement, even if they were likely to be avail- 
able for such a purpose by indicating natural groups 
or affording additional means of characterising them. 
“ Some of them,” says Dr. Boisduval, “ such as 
those of Machaon, Alcxanor, Asterias, are cylindri- 
cal and smooth ; others (Crassus, Philenor), are 
protected with rather long fleshy prominences ; in 
a very- great number ( Pammon , Memnon, C hale has, 
&c.) the two first segments are attenuated, and 
capable of being retracted under the third and 
fourth, which are dilated and often ornamented 
with ocular spots analogous to those presented by 
