ENTOMOLOGY. 
105 
various organs are, of course, greatly modified, some 
being more fully developed, and others becoming 
almost or wholly obsolete. Three principal types of 
form in the construction of the mouth prevail among 
haustellate insects, which have received the names 
of Promuscis, Proboscis, and Haustellum. Each of 
these is characteristic of a particular order, and will 
therefore demand a detailed examination in the sub- 
sequent exposition of the peculiar characters of these 
orders ; at present it may he merely remarked, that 
the tube for the transmission of the fluids is generally 
formed by the elongation of the maxillae, accompanied 
with some accessory parts, sometimes the upper, at 
other times the under lip forming a lengthened sheath 
to support and protect the other parts. 
The next primary division of an insect which re- 
quires attention is that which may he described gene- 
rally as lying between the head and abdomen, viz. 
the Thorax. It is a highly important part, in as much 
as it bears all the organs of motion, and determines 
in some degree the whole shape of the insect ; the 
variety of its forms and the multitude of pieces en- 
tering into its composition, render the study of it 
rather difficult, and this difficulty has been increased 
by the complex nomenclature which has been assigned 
to its parts. A slight inspection suffices, for the most 
part, to shew that it is made up of three principal 
parts ; the anterior of these, bearing the fore-legs, is 
termed the prothorax ; the next, which supports the 
middle-legs and the fore- wings, (in such species as 
are provided with four wings,) is the mesothorax ; 
