xi PHYLUM ARTHROPODA 609 



glands ; the common duct thus formed opens into the buccal 

 cavity (Fig. 503). 



From the buccal cavity there proceeds backwards a narrow 

 oesophagus (ces.), which leads to an elongated 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 or mesenteron a 

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

 off eight tubular hepatic cceca (hep. CCB.) blind tubes somewhat 

 narrower than the stomach. The point of junction of the stomach 

 with the intestine is marked by the presence of very numerous 

 thread-like yellow appendages the Malpighian tubes (malp.) 

 which are the renal organs of the animal. The intestine (int.) 

 terminates in a dilated portion the rectum (ret.) the walls of 

 which are longitudinally folded. Of the entire alimentary 

 canal only a small part the stomach with the appended 

 hepatic caeca, is of the nature 

 of a mesenteron, the region in 

 front being a stomodaeum, 

 and that behind a procto- 

 daeum. 



The heart, with the aorta 

 into which it is continued in 

 front, is the only part of the 

 blood-system with definite 

 walls. It is an elongated 



tube, closed behind, Open in FIG. i303. Right salivary gland-and salivary recep- 

 P . tacle of Cockroach. (After Miall and Denny.) 



front, running along the 



middle line of the abdomen and thorax immediately beneath the 

 terga, enclosed in a pericardial sinus which, as in the Crayfish, is 

 part of the haemoccele. Internally the tube is divided by valves 

 opening forwards into a number of chambers ; its walls are perforated 

 by a series of pairs of valvular apertures or ostia. Running from 

 the wall of the heart to the terga are a series of segmentally-arranged 

 fan-shaped bundles of muscles the alary muscles (Fig. 533, m.). 

 T^eSe fibres are partly inserted into the wall of the heart, the 

 -iumen of which they dilate, partly into a membrane underlying the 

 pericardial sinus. 



Respiration takes place through the instrumentality of a 

 system of air-tubes or trachece (Figs. 504 and 505), opening on the 

 surface at the stigmata, to which reference has already been made. 

 These tracheae form a richly ramifying system extending to all 

 parts of the body. They possess a chitinous internal lining, 

 supported by means of a spirally-wound, fibre-like thickening. By 

 means of this system of air-tubes air is conveyed throughout the 

 body to all parts, and there is thus ensured the rapid and 



