624 



ZOOLOGY 



SECT. 



The principal sets of muscles of the trunk of the Cockroach 

 are (1) the longitudinal sternal muscles (Fig. 494, long, stern.), 

 which form a transversely segmented sheet, extending between 

 adjoining sterna of the thorax and abdomen: (2) oblique sternal 

 muscles (obi. stern.), confined to the abdomen ; and (3) longitudinal 

 tergal muscles, best developed in the abdomen. The various 

 segments of the limbs are capable of being flexed or extended on 

 one another, as in the Crayfish, by the contractions of special 

 muscles. The wings are little used, the female Cockroach being 

 incapable of flight, and the male not a strong flier : accordingly 



the wing muscles are not very 

 strongly developed. 



Between the body-wall and 

 the alimentary canal is a cavity 

 taking the place of the coelome, 

 but in reality forming a speci- 

 ally developed part of the 

 blood-vascular system (hcemo- 

 <-<i'/e). This is bounded extern- 

 ally by an irregular wall, formed 

 of a mass of polygonal cells 

 constituting the fat-body. 



Digestive system. The 

 mouth opens into a buccal 

 cavity, which receives the ducts 

 of the salivary glands (Fig. 495, 

 sal. gld.}. Each gland is divided 

 into two lobes, each made up 

 of numerous ramifications. In 

 close relation to each gland is 

 an elongated thin-walled sac- 

 the salivary receptacle (sal. rcc.). 

 The duct given off from the 

 salivary receptacle joins that 

 of the opposite side, and the 

 median duct thus formed is 

 joined by a single duct (sal. du.), formed by the union of the two 

 ducts of the salivary glands ; the common duct thus formed 

 opens into the buccal cavity (Fig 496). A chitmous fold of 

 the floor of the mouth forms the lingua or tongue. 



From the buccal cavity there proceeds backwards a narrow 

 oesophagus (ces.), which leads to an elongated saccular dilatable sac 

 -the crop (cr.). On this there follows the proventriculus or 

 gizzard (gizz.) a pear-shaped chamber with the broad end directed 

 forwards, its chitinous internal lining raised up into a number of 

 teeth. A narrow passage leads from this to the stomach- 

 a wide tube with glandular walls ; from its anterior end are 



long, stern 



ebl stern, 

 terg. stern, 



Fio. 494. Ventral portion of the muscular 

 system of the Cockroach, add. cox. ad- 

 ductor of coxa ; abd. cox. abductor of coxa ; 

 ext. fern, extensor of femur ; 1st terfi. fttern. 

 first tergo-sternal ; long, stern, longitudinal 

 sternal ; obi. stern, oblique sternal. (After 

 Miall and Denny.) 



