420 ESSENTIALS OF ZOOLOGY 



end ; the outer lobe or galea; and the maxillary palpus. The caudal 

 part of the mouth parts is the lower lip or labium, which is composed 

 of the suhmentu7n which acts as a hinge on the epicranium above; 

 a mentum; labial palpi, and two large outer flaps, the ligulae. 



The prothorax is the segment to which the head it attached. It may 

 be divided into two regions, the dorsal part known as the pronotum 

 and the ventral portion known as the sternum. The pronotum is a 

 saddle or bonnetlike piece extending over the dorsal and lateral 

 regions of the prothorax. It is made up of a fusion of four plates, 

 which are indicated by the transverse sutures. The sternum or ven- 

 tral side of the pronotum is also made up of separate plates, or 

 sclerites. The anterior sclerite bears a spine on the median line. 



The next two segments, the mesothorax and metathorax, are made 

 up of sclerites that are intimately associated. Their structure 

 will be discussed together. The mesothorax is joined to the pro- 

 thorax by a membrane which permits of more or less movement. 

 Posteriorly the metathorax is joined immovably wdth the first ab- 

 dominal segment. The mesothorax and metathorax form a strong, 

 boxlike structure for the support of the w^ing and leg muscles. Like 

 the prothorax these segments are made up of separate plates, held 

 together by a tough, connecting membrane. These plates may, how- 

 ever, be divided into three groups : the tergum, or dorsal region ; 

 the sternum, or ventral region; and the pleuron, or lateral region. 

 On the dorsal and ventral regions of the body the sutures separat- 

 ing the mesothorax from the metathorax are not very distinct. On 

 the sides of the body, however, there is a very distinct line, or 

 suture, running from the posterior border of the attachment of the 

 second pair of legs toward the dorsal part of the body. This suture 

 divides the mesothorax from the metathorax. The pleura of each 

 of the posterior thoracic segments are again divided by transverse 

 sutures, so that each pleuron consists of two sclerites. 



A pair of legs arises from the lateral and ventral portions of each 

 of the segments of the thorax. Each leg is composed of five parts. 

 The coxa is the first segment and is attached to the thorax by a tough 

 elastic membrane. The next segment, the trochanter, is a very short 

 piece which is hard to distinguish except in the first pair of leers. 

 The femur is the third and largest segment of the leg, and in the 

 case of the metathoracic leg contains the muscles used in jumping. 

 The fourth segment, the tihia, is slender, but about the same length 



