BLATTA. 225 



which is the lacinia or blade and the outer the galea or 

 hood, and a long jointed exopodite usually known as the 

 maxillary palp. The second maxillce closely resemble the 

 first maxillae in structure, but the labial palps (or exopodites) 

 are smaller and the protopodites are fused across the 

 middle line, as noticed above, the two appendages forming 

 the labium. The head is joined by a neck with small 

 sclerites to the thorax. The thorax has three segments, 

 called the prothorax, the mesothorax and the 7netathorax. 

 These are freely movable. Each has a pair of legs on the 

 ventral surface, hence the cockroach has three pairs of 

 legs. Each has a basal piece or coxa^ a small trochanter^ a 

 long femur and tibia^ and a six-jointed tarsus terminating in 

 two claws. On the dorsal surface of the male the mesothorax 

 bears a pair of leathery wings (sometimes termed elytra)^ 

 and the metathorax carries a pair of membranous wings. 



The abdominal segments, like those of the lobster, are 

 movable, and each has a tergon and sternon. There are 

 ten abdominal segments. The terga overlap each other, 

 and the 7th completely overlaps the small 8th and 9th ; 

 hence one can only, count eight (i to 7 and 10). 

 The last or loth is notched, and bears laterally a pair of 

 many-jointed anal cerci. Of the nine sterna, the first is a 

 mere rudiment and the 9th in the male bears a pair of 

 small styles. In the female, the 7th is boat-shaped and 

 envelopes the sterna behind it which are adapted for sexual 

 functions. Hence in the female only seven sterna can be 

 made out externally. At the hind end of the body the anus 

 opens and below it is the opening of the genital organs. 

 There are no excretory pores, but the respiratory organs or 

 tracheae open by ten paired apertures, the stigmata. Two of 

 these open laterally between the thoracic segments, and the 

 other eight lie between the terga and sterna of each of the 

 first eight abdominal segments. Air is inhaled and exhaled 

 through these stigmata by a rhythmic lengthening and 

 shortening of the segments upon each other (caused by 

 tergal and sternal muscles). 



The external features show a marked contrast to those of the 

 lobster. The principal differences are (i) the presence of only one pair 

 of antennae ; (2) only three pairs of thoracic appendages ; (3) the absence 

 of abdominal appendages (except, perhaps, the anal cerci) ; (4) the 

 M. 16 



