HARDWICKE'S SCIENCE-GOSSIP. 



109 



the five-jointed palp forms a flexible limb used in the 

 prehension of food and in exploration ; the lacinia 

 carries a double-pointed tooth of dense chitin, while 

 the galea is soft, clothed with fine setoe, and probably- 

 sensory in function. 



On the hinder surface of the head, below the 

 occipital foramen, is the labium, which represents 

 the second pair of maxillae, fused together in their 

 basal half, but retaining elsewhere sufficient resem- 

 blance to the less-modified anterior pair to permit of 

 the identification of its component parts. The palp 

 is three-jointed, and carried upon a separate basal 



side, and two ventral. The peculiar shape of the 

 lateral and ventral plates may be seen in fig. 63. 



The elements of the thoracic exoskeleton are 

 simpler in the cockroach than in insects of powerful 

 flight, where adaptive changes greatly obscure the 

 primitive arrangement. There are three segments, 

 each defended by a dorsal plate {tergum) and a ventral 

 plate (sternu;n). The sterna are often divided into 

 lateral halves. Of the three terga the first (pronotum\ 

 is the largest ; it has a wide free edge on each side, 

 projects forwards over the neck, and when the head 

 is retracted, covers this also, its semi-circular fore- 



Fig. 65. — Leg of A orientalis; ventral surface, ex, coxa ; yif, femur; tl>, tibia; 

 ta, tarsus ; small joint between coxa and femur, trochanter. X 3- 



Fig. 64. — Head of P. orientalis ; 

 side view, oc, eye ; ^e, gena ; 

 fim, mandible. X 10. 



Fig. 66. — Wings and wing-cases of male Cockroach. X 4- 



joint, or palpiger, and the lacinia and galea (known 

 as paraglossse) are readily made out. 



We cannot here discuss the difficult question as to 

 the theoretical composition of the head. It bears 

 three pairs of appendages which unquestionably 

 denote as many typical segments ; the antennse, 

 though not developed precisely in the same way or 

 from similar parts, may be taken to represent a 

 peculiar fourth segment, but there is no reason to 

 suppose that other segments are represented in the 

 head of any insect. 



The neck is a narrow cylindrical tube, with a 

 flexible wall, strengthened by eight plates, viz., two 

 dorsal (slightly united together), two lateral on each 



edge then forming the apparent head-end of the 

 animal. All the terga are dense and opaque in the 

 female ; in the male the middle one {tnesonohitn) and 

 the hindmost (inetanoliim) are thin and semi-trans- 

 parent, being ordinarily overlaid by the wing-cases. 

 While the thoracic terga diminish backwards, the 

 sterna increase in extent and firmness, proi^ortionally 

 to the size of the attached legs. The prosternum is 

 small and coffin-shaped ; the mesosternum partly 

 divided into lateral halves in the male, and completely 

 so in the female. The metasternum is completely 

 divided in both sexes, while a median piece inter- 

 venes between its lateral halves in the male. Behind 

 the sterna, especially in the case of the second and 



