STRUCTURE, METAMORPHOSES, ETC., OP COLEOPTERA. 10 
external spiracles or stigmata, and the internal 
tracheae or air-tubes ; iu rare cases gills or branchice 
are present in certain larvae (e.g. Gyrinus, Berosus, 
&c.). 
The attachments and development of the muscles 
of the Cockchafer, a good type of the beetle tribe, are 
admirably described and figured in Strauss-Diirck- 
heim’s “ Considerations generales sur l’Anatomie com- 
paree des Animaux articules ” (Paris, 1828). 
Presuming that the student now has a general idea 
of what is signified by the word Coleoptera, we will, 
before entering more fully into the subdivisions of that 
order, proceed to make some observations upon certain 
points which it will be necessary for him to master, — 
such as the definition of a species, &c., the terms used 
in descriptions, the names of external parts of the body, 
the best books of reference, and the instruments 
required, &c. 
A “ species,” the most simple lasting alliance of 
specimens that is usually recognized (commonly termed 
a “ sort ” or “ kind ”), may be defined as an imaginary 
congregation of individuals, possessed, during all the 
stages of their existence, of an identity of habit and 
structure, and of which the sexes confine themselves to 
each other in breeding. 
A “ genus ” consists of an assemblage of such 
species, usually somewhat alike in habits, as possess in 
common either one well-defined structural character, 
or several of a minor nature, unaccompanied by any 
radical points of separation. 
In a similar way, subfamilies, families, tribes, sec- 
tions, orders, and classes are constituted ; the points 
of affinity iu each become more and more remote as 
c 2 
