16 



PARASITES OF THE DOMESTIC ANIMALS 



The mouth parts (Fig. 4) undergo great modification, though all may 

 be referred to a common type. This is well presented in its primitive 



condition by the grasshopper, 

 in which we have the labrum, 

 or upper lip, represented b}' a 

 broad unpaired plate situated 

 in front of the mouth. Under 

 the labrum is a parr of strong- 

 jaws, the mandibles, each con- 

 sisting of a single unsegmented 

 piece with a cutting innei' edge, 

 the two having a lateral move- 

 ment. Following the mandibles 

 is the first pair of maxillae which 

 are prehensile and gustatory in 

 function. These have a num- 

 ber of joints and bear curved 

 and segmented palpi. The sec- 

 ond pair of maxillae are fused 

 to form a single plate, — the la- 

 bium, which is accessory in func- 

 tion to the first pair of max- 

 illae, and, like the latter, bear a 

 pair of segmented palpi. The 

 labium forms the posterior and 

 the labrum the anterior bound- 

 ary of the mouth. 



The thorax (Fig. 1) has three 

 a middle, — the. mesothorax, 



Fig. 1. — Diagram of an Insect, with Head and 

 Thoracic Segments Disarticulated: a, head, 

 bearing compound eyes, simple ocelli, and 

 antennae; b, prothorax; c, mesothorax; d, meta- 

 thorax; e, abdomen; f, ovipositor. The pro-, 

 meso-, and metathorax each bear a pair of legs; 

 the meso- and metathorax each a pair of wings. 

 1, Coxa; 2, trochanter; 3, femur; 4, tibia; .5, tar- 

 sus, terminating in a claw (after Orton, by 

 Dodge; Copyright, 1894, by Harper & Brothers). 



segments, an anterior, — the prothorax 



Fig. 2. — Diagram of the Principal Internal Anatomical Parts of an 

 Insect: m, mouth; or, crop; st, stomach; i, lower portion of intestine; 

 a, anus; h, heart; s, salivary glands; c, cerebral ganglion; n, ventral 

 ganglion; Mp, Malpighian tulDules; o, ovaries; g, genital aperature (after 

 Boas, by Kirkaldy & Pollard). 



and a posterior, — the metathorax. 

 somewhat fused. 



The last two of these are usuallv 



