VI INTRODUCTION. 



II., 96I). 4th. Mouth-parts. The mouth-parts con- 

 sist of an upper lip, labruin, an under lip, labium, 

 and two pairs of jaws acting horizontally between 

 them. The upper pair of jaws are called the mandi- 

 bles, the lower pair the maxillce. The maxillse and 

 lower lip are each furnished with a pair of feelers, 

 called respectively the maxillary palpi, ^nd the labial 

 palpi. The lower lip supports also the tongue, ligula, 

 which is composed of three parts, one central, glossa, 

 or lingua, two lateral, paraglossce. That part of the 

 lower lip which supports these organs is called the 

 menUim. 



Thorax. — Consists of three segments,— />w//i:^rrt,r, 

 mesothorax and nietatliorax. 



Appendages of the thorax. — ist. Legs, six in num- 

 ber, two to each segment ; each composed of the fol- 

 lowing parts, — coxa, trochanter, femur, tibia, and tar- 

 sus. The tarsus is from feWto six, usually five, jointed, 

 and terminated by claws. 2nd. Wings, two pairs, 

 one mesothoracic, the other metathoracic ; they are 

 not always present, and are sometimes deciduous. 



Abdomen. — Consists of about nine segments, though 

 Packard states that the typical number is eleven. 



INTERNAL ANATOMY. 



Skeleton. — No internal skeleton as with Vertebrates. 

 The external covering of the insect is hardened by the 

 deposition of chitine, and serves as a framework for 

 the attachment of muscles. Note, however, internal 

 processes of the body wall for the attachment of mus- 

 cles. 



Muscular system. — The muscles are very numerous. 

 Lyonnet describes 3,993 in a single caterpillar. They 



