372 



PHYLUM ARTHROPODA 



External Characters 



Region. 



The head is ver- 

 tically elongated 

 and separated 

 from the thorax 

 by a neck. 



The insect's 

 head seems to 

 consist of seven 

 fused segments^ — 

 ocular, an teniiary, 

 intercalary, man- 

 dibular, maxillu- 

 lar.maxillary, and 

 labial. 



Appendages. 



The thorax con- 

 sists of three seg- 

 ments — 



(a) prothorax, 



(b) mesothorax. 



(c) metathorax. 



(Each segment 

 is bounded by a 

 dorsal tergum 

 and ventral ster- 

 num.) 



The ' abdomen 

 consists of lo 

 (or ii) distinct 

 segments, with 

 terga and sterna 

 as in the thorax. 

 The first sternum 

 is rudimentary in 

 both sexes, and 

 in the female the 

 eighth and ninth 

 segments are con- 

 cealed by the 

 large seventh. 



1. The antenna (probably homologous 

 with appendages), long, slender, many- 

 jointed, tactile. 



2. A pair of stout toothed mandibles 

 working sideways. 



3. The first maxilla;, each consisting — 

 (a) of a basal piece or protopodite with two 

 joints : a basal cardo, a distal stipes ; 



(b) of a double endopodite borne by the 



basal piece, 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 consist- 

 ing of five joints. 



4. The second pair of maxillae, fused to- 

 gether as the " labiuin," consisting — (a) of a 

 fused basal piece or protopodite with two 

 joints : a basal sub-mentum, a smaller distal 

 mentum ; on each side this protopodite 

 bears^ 



(b) a double endopodite (ligula) consisting 

 of an inner lacinia and an outer 

 paraglossa ; 



(c) an exopodite or labial palp, consisting 

 of three joints. 



(a) First pair of legs. 



(b) Second pair of legs. 



(c) Third pair of legs. Each leg consists 

 of many joints — a basal expanded 

 " coxa " with a small " trochanter " at 

 its distal end, a " femur," a '' tibia," 

 a six-jointed tarsus or foot ending in a 

 pair of claws (Fig. 212). 



Two cigar-shaped tactile anal cerci, at- 

 tached under the edges of the last tergum, 

 are possibly relics of the last abdominal 

 appendages. 



The ninth sternum of the male bears a 

 pair of styles, possibly relics of appendages. 



Both sexes have complex hard structures 

 (gonapophyses) beside the genital apertures. 

 They are possibly relics of appendages. 



Other Structures. 



The large black compound 

 eyes. 



The " upper lip " or labrum, 

 in front of the mouth. 



The white oval patches near 

 the bases of the antenna;, pos- 

 sibly sensory. 



In some primitive insects a 

 minute pair of appendages, 

 known as maxillulae, occurs 

 between the mandibles and the 

 first maxillae. 



(b) A pair of wing-covers (modi- 

 fied wings), rudimentary in 

 female of P. orientalis. 

 (f) 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 respira- 

 tory apertures or stigmata. 



A pair of stigmata occur be- 

 tween the edges of the terga and 

 sterna in the first eight abdo- 

 minal segments. 



The anus is tenninal, beneath 

 the tenth tergum of the abdo- 

 men ; a pair of " podical plates " 

 lie beside it. 



The genital aperture is on the 

 eighth segment in the female, 

 behind the niiath sternum in the 

 male. 



The opening of the sperma- 

 theca — the female's receptacle 

 for spermatozoa — lies on the 

 ninth sternum of the abdomen. 



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