530 



ZOOLOGY 



duced along its inner edge into strong teeth. The mandibles lie 

 one on each side of the mouth, and are so articulated that, by 

 means of muscles, their toothed edges can be brought together in 

 the middle line, so as to rend the food. 



The fourth and fifth appendages are very small, and are prob- 

 ably functionless or nearly so : they follow one another just behind 

 the mandible, and are called the first and second maxilla;. The 

 first maxilla {4-) consists of two curved chitinous plates, the second 

 of a basal portion produced into two branches (5). Betvi^een the 

 first maxilla and the mandibles are a pair of delicate unjointed 



l.Antennula 

 2. Anr ennj 



/2 "^^^B-.B,^,,,,,-^^ 



a.7!''ThopacioFoot 



10.i;'AbdominalFooh 



Fig. 423. — Typical appendages of Apus. 1 — /t, podomeres of axis ; hr. bract ; en. 1, en. 7, eiidites ; 

 Jl. flabellum ; ov. ova. (After Lankester.) 



processes, the par agnatha (Fig. 421, 2ogn.): they form together a 

 sort of lower lip, and are not usually reckoned as appendages. 



The foregoing appendages all spring from the unsegmented 

 anterior portion of the body or head. As we shall see, however, 

 the succeeding limbs arise each pair from its own segment, so 

 that the presence of five pairs of appendages on the head may 

 be taken provisionally as an indication that this region of the 

 body is composed of five fused segments. 



The sixth appendage (6') springs from the ventro-lateral region 

 of the first clearly marked segment, and is the first of the long 

 row of appendages plainly visible in a ventral view. It consists 

 of an ««s formed of four podomeres (7-4), and bearing a number 

 of offshoots : six of these, called endites {en. 1 — en. G), arise from 



