420 



THE INVERTEBRATA 



adult, including a preoral and (between the antennae and the mandibles) 

 an intercalary. All segments except the first are originally postoral 

 but in development the mouth moves back and comes to lie between 

 the mandibles. The number of head segments is the same as in the 

 embryo insect and the crustacean, and a remarkable homology may be 

 observed between the chilopod and insect head appendages. Thus 



hd.c- 



/-. 



/ / 



ant. 



Abr. 



^md. 



.^- 



mx- 



hd.c. 



t.mxp.- 



/..-./Y^^Qx^ 



mxp. 



I 



Fig. 296. Ltthobiusforficatiis. Original. Ventral view of head and two succeed- 

 ing segments in a specimen boiled in potash and mounted in Canada balsam. 

 On the right of the observer the maxilliped, and the sternum belonging to it, is 

 lightly stippled : on the left the maxilla is more coarsely stippled, ant. antenna ; 

 amb. I , base of the first ambulatory appendage ; hd.c. head capsule ; Ibr. labrum ; 

 md. mandible ; mx. maxilla ; ?nx.' first maxilla ; mxp. maxilliped (poison claw) ; 

 t.mxp. tergum of the maxilliped. 



the antennae are jointed mobile appendages varying in length; the 

 mandibles are toothed plates without palps, the ist maxillae consist of 

 a basal portion bearing inner and outer lobes, while the 2nd maxillae 

 are usually fused together to form a sort of labium and possess a 

 palp-like jointed structure (Fig. 296). The difference between the 

 mouth parts of an orthopteran insect and a chilopod lies in the 

 reduction in size of the two pairs of maxillae in the latter, which 



