138 ZOOLOGY. 
plate, as it has an articulated palpus on each side, much like those of the © 
former organs. The labium is partly covered by and articulated with the 
mentum, which is articulated to the anterior part of the craniwm, beneath 
named the yugulwm. The labial palpi are attached one on each side of the 
labium near the tongue. The projecting sides of the tongue are named 
paraglosse. | 
Thorax. The thorax supports the organs of motion, and is attached to the 
head of an insect by a membranous connexion. Its entire upper and lower 
surfaces are named respectively tergum and pectum. It is composed of 
three divisions, named prothorax, mesothorax, and metathorax ; the upper 
surfaces of which are termed pronotum, mesonotum, and metanotum, — 
and the inferior surfaces antepectus, medupectus, and postpectus.* The 
prothorax bears the anterior pair of feet, but as it bears no wings it is 
simpler in its structure, and its theoretical parts are more difficult to discover 
than those of the two other thoracic segments. It is in the latter, therefore, 
that we must look for the subdivisions of these segments. These are 
generally enumerated from the front backwards, when the four subdivisions 
of the upper part will be the prescutum, scutum, scutellum, and postscu- 
tellum, and those below, the paraptera, sternum, eprsterna, and epimera. 
The term pleura is applied to the sides in descriptions, but it is not limited 
to any particular part. The sternum is the chief central part with which 
the two episterna articulate, and the two epymera are near the insertion of 
the feet, and the paraptera (or tegule, or patagia) near the wings. New- 
port thinks it exists in a rudimentary condition in the prothorax, but Straus 
Dirckheim thinks the part referred to by that author is the rudiment of 
another segment. The mesothoracic scutellum is often seen wedged 
between the base of the elytra in the Coleoptera (pl. 81, figs. 23, 124, 131, 
&c.) The prothorax and mesothorax have usually each a pair of spiracles, 
but in the Hymenoptera the second pair is upon the metathorax. 
The chief appendages of the thorax are the feet, which are never absent. 
These organs have many modifications to adapt them to their various uses 
ot walking, swimming, grasping, leaping, digging, &c. The thoracic 
cavities into which the base of the feet is fitted are named acetabula, and 
the basal part of the limb which enters them is the cova; but this is 
sometimes firmly attached, so as to have no independent motion. Next to 
the coxa follows a small articulation named the trochanter ; then follows 
the principal articulation, the femur, or thigh, to which succeeds the ébza, 
which is often armed at the end with fixed or movable spines, named 
calcuria. ‘This part is more generally provided with spines and cilia than 
the other parts. The tibia is followed by the tarsus, which is made up of 
several small articulations named phalanges, of which there are never more 
than five. The end of the tarsi is usually armed with two claws named 
ungues. 
* Prostethus, dc., would be more uniform with prothorax, dc., than antepectus. The name 
prosternum cannot be used with propriety, as it is applied to a minor division (sternum, episterna) 
of the breast of each thoracic segment. 
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