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 by a 

 broad unpaired plate situated 

 in front of the mouth. Under 

 the labrum is a pair of strong 

 jaws, the mandibles, each con- 

 sisting of a single unsegmented 

 piece with a cutting inner 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- 



FiG. 1. — Diagram of an Insect, with Head and bium, wMch is aCCeSSOry in func- 



Thoraoio Segments Disarticulated: a head ^^^^ ^^ ^^le first pair of max- 



beariug compound eyes, simple ocelli, and . j n +u i ++ u 



antennae; b, prothorax; c, mesothorax; d, meta- lliSS, and, llKe tne latter, bear a 



thorax; e, abdomen; f, ovipositor. The pro-, pair of Segmented palpi. The 



meso-, and metathorax each bear a pair of legs; ]„u,-„™ fr)vm=i +hp nr.c!+prinr nnd 



the meso- and metathorax each a pair of wings. i^Drnm lorms tne posterior ana 



1, Coxa; 2, trochanter; 3, femur; 4, tibia; 5, tar- the labrum the anterior bound- 



sus, terminating in a claw (after Orton, by ^rv of the mOUth 

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



segments, an anterior, — the prothorax, a middle, — the mesothorax. 



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

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

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

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

 Boas, by Kirkaldy & Pollard). 



and a posterior, — ^the metathorax. 

 somewhat fused. 



The last two of these are usually 



