116 MANUAL OF ANIMAL BIOLOGY 



habits. In other words, the adaptation is very marked. In 

 general, it may be said that there are two main groups of Insect 

 mouth parts, with a great number of sub- varieties of each, and 

 these are designated as the biting type (mandibulate) and suck- 

 ing type (suctorial). The mouth parts of the Grasshopper as 

 described above are mandibulate, and are particularly adapted for 

 crushing the plant tissues on which this animal feeds. Those of 

 the Bee, which will be described in the next section, are of the 

 suctorial type and are particularly adapted for sucking the nectar 

 from flowers. However, the mandibles of the Bee are also very 

 well-developed and function in the manipulation of pollen grains 

 and wax. In the Mosquito, suctorial mouth parts, which are de- 

 signed solely for piercing and sucking, may be seen. 



2. Thorax 



The thorax of the Grasshopper, and of Insects in general, consists 

 of three segments, the anterior of which is termed the prothorax, 

 and then follow the mesothorax and the metathorax in the 

 order named. Each of these segments bears a pair of legs, and, 

 in addition, a pair of wings is found on each of the two posterior 

 thoracic segments. (W. f. 54.) 



The exoskeleton covering the thorax is divided into a dorsal 

 portion (tergum), a lateral portion (pleurum), and a ventral 

 portion (sternum) . The tergum and pleurum are subdivided into 

 a number of sclerites. 



Wings. The wings of the anterior, or mesothoracic, pair are 

 large and of a resistant leathery nature. When at rest they lie 

 over and protect the posterior, or metathoracic, pair. The latter 

 are delicate membranous structures which fold fanwise when at 

 rest. They are adapted for flying, and, when extended, a support- 

 ing framework of 'veins' can be seen ramifying throughout the 

 wing tissues. The wings are operated by powerful muscles which 

 are enclosed within the thorax. 



Legs. The three pairs of legs are named in accordance with the 

 thoracic segment to which they are attached ; that is, the protho- 

 racic, mesothoracic, and metathoracic, legs. The general structure 

 of all is essentially the same, but the metathoracic legs are larger 

 than the other pairs. Each leg consists of five segments. These 

 are: (a) the coxa which forms the attachment with the body; 

 (6) the small trochanter ; (c) the large femur which constitutes 



