276 



ARTHROPODS. 

 External Characters. 



The Head. 



is vertically 

 elongated and 

 separated from 

 the thorax by a 

 neck. 



The Thorax. 

 It consists of three 



segments : — 

 (a) prothorax, 

 (5) mesothorax, 



ifi) metathorax. 



(Each segment is 

 bounded by a 

 dorsal tergum, 

 and ventral ster- 

 num.) 



The Abdomen. 



It consists of ten 

 distinct seg- 

 ments, with 

 tergaand sterna 

 as in the thorax. 



Appendages of the Head. 



1. A pair of stout toothed mand- 



ibles working sideways. 



2. The first maxilla;, each con- 



sisting (a) of a basal piece or 

 protopodite with two joints— 

 a basal cardo, a distal stipes ; 

 ip) of a double endopqdite 

 borne by the baisal jjiece, 

 and consisting of an inner 

 lacinia and a softer outer 

 galea ; 

 (c) of an exopodite or maxillary 

 palp also borne by the basal 

 piece, and consisting of 

 five joints. 



3. The second pair of maxillee, 



fused together as the "labi- 

 um," consisting {a) of a fused 

 basal piece or protopodite 

 with two joints — abasalsub- 

 mentum, a smaller distal 

 mentum ; on each side this 

 protopodite bears 

 {K) a double endopodite (ligula) 



consisting of an inner 



lacinia, and an outer para- 



glossa ; 

 ((t) an exopodite or labial palp, 



consisting of three joints. 



The Appendages of the 

 Thorax. 



{a) First pair of legs. 

 (^) Second pair of legs. 



(c)Third pair of legs. Each leg con- 

 sists of many joints — aljasal 

 " coxa " with a small " troch- 

 anter" at its distal end, a 

 "femur," a "tibia," a six- 

 jointed tarsus or foot ending 

 in a pair of claws. 



Appendages (?) of the 

 Abdomen. 



Two cigar-shaped tactile anal 

 cerci, attached under the 

 edges of the last tergum, 

 are possibly relics of abdom- 

 inal appendages. 



The ninth sternum of the male 

 bears a pair of styles, possibly 

 relics of appendages. 



Both sexes have complex hard 

 structures (gonapophyses) be- 

 side the genital apertures. 

 They are possiby relics of 

 appendages, but this is not 

 very likeiy. 



Other Structures on the 

 Head. 



The antennse (probably not 

 homologous with append- 

 ages), long, slender, many- 

 jointed, tactile. 



The large black compound 

 eyes. 



The "upper lip" or labrum, 

 in front of the mouth. 



The white oval patches near 

 the bases of the antennae, 

 possibly sensory. 



Other Structures on the 

 Thorax. 



{b) A pair of elytra or wing- 

 covers (modified wings) ; 

 rudimentary in female of 

 P. 07~ientalis, 



(c) A pair of membranous 

 wings, sometimes used in 

 flight, folded when not in 

 use, absent in female of 

 P. orientalis. 



Between the segments of the 

 thorax are two pairs of 

 respiratory apertures or 

 stigmata. 



Other Structures on the 

 Abdomen. 



A pair of stigmata occur bc' 

 tween the edges of the 

 terga and sterna in the 

 first eight abdominal seg- 

 ments. There are there- 

 fore twenty stigmatain all. 



The anus is terminal, beneath 

 the tenth tergum of the 

 abdomen ; apairof "podi- 

 cal plates " he beside it. 



The genital aperture is ter- 

 minal, ventral to the anus. 



The opening of the sper- 

 matheca — the female's 

 receptacle for sperma- 

 tozoa—lies on the ninth. 

 sternum of the abdomen. 



