The Cockroach. 



53 



latter articulates, first, the endopodite, divided longitudinally 

 into two pieces, an inner lacinia and an outer galea. The 

 exopodite is a five-jointed palp. The second maxillce have 

 their protopodites fused to form a basal piece, divided into a 

 submetitum above and a mentum below; the endopodite is 

 divided into a paraglossa (or lacinia) and a galea; while, 

 as in the first maxillae, the exopodite is a palp, but three- 

 jointed. 



The three pairs of thoracic appendages (whence the term 

 " Hexapoda" for insects) are walking limbs with five joints apiece 

 and a pair of terminal claws. The abdomen has no obvious 

 appendages ; but the cerci borne on the tenth segment and the 

 anal styles of the male on the ninth may be vestiges of such 

 structures. 



The remaining characters of importance to be noted without 

 dissection are the orifices of the tracheje and' of the scent 

 glands. The former — the stigmata or spiracles — are present to 

 the number of nine or ten pairs— two upon the thorax, and the 

 rest upon the abdomen. They are widish orifices, guarded by 

 hairs, which lie laterally between the segments, and lead into 

 the tracheal tubes, which ramify in the interior of the body, 

 and will be described presently. The scent glands, which have 

 been only lately discovered, are two pouches lying on the 

 dorsal surface of the fifth abdominal segment, between this 

 segment and the next behind. 



The heart is a dorsally situated tube which ends blindly 

 behind, and is prolonged into an aorta anteriorly. The heart 

 has a series of paired lateral ostia, and lies in a blood space 

 like that of Astacus. But the circulation generally of Blatta is 

 less " finished " than that of Astacus. In addition to the pulsa- 

 ting sinus which envelops the heart, there is a ventral sinus, also . 

 pulsating, which covers the nerve-cord. 



The respii-atory organs are the tracheae. These are tubes 

 lined with a spirally thickened chitinous membrane, which 

 ramify through the body, as shown in Figs. 27 and 28. Air is 

 thus carried to every organ ; and this complete aeration perhaps 

 accounts for the imperfection of the circulatory system, which 

 is usually the only, or nearly the only, way in which the organs 



