RESPIRATORY SYSTEM 163 



Having made out the anatomical relations of the salivary 

 glands, receptacles, and ducts, remove the whole apparatus. 

 Stain it with carmine or magenta ; mount it in water, and 

 examine with the microscope. 



Nuclei are visible in the walls of the ducts, 

 and in the secretory cells of the glands. 



The chitinous lining of the "ducts shows a 

 spiral thickening. 



b. The ' hepatic ' caeca are eight or seven caecal diver- 

 ticula of the anterior end of the mesenteron. 

 They are convoluted and club-shaped. 



Note the openings of the hepatic cceca into the mesenteron. 

 3. The excretory system consists of sixty or more Malpighian 

 tubules, which are fine filamentous diverticula of the 

 anterior end of the ileum, arranged in six bundles. 

 They are very long and convoluted, and are inter- 

 laced among the tracheae and the filaments of the 

 fat-body all through the abdomen. 



C, The Respiratory System. 



The respiratory system consists of a series of tracheal tubes 

 containing air. These commence at the respiratory apertures, 

 or stigmata, on the sides of the thorax and abdomen, and 

 ramify through all parts of the body. Expiration is effected 

 by contraction of the muscles of the body, which compress 

 the tracheae ; inspiration, by dilatation of the tracheae through 

 the elasticity of their cuticular lining. 



The readiness with which air is carried to all parts of the 

 body, through the great perfection of the respiratory system, 

 accounts for the extreme imperfection of the circulatory 

 system in an animal which is otherwise very highly organised. 



1. The tracheal tubes when full of air are silvery white. 

 Remove a large trachea, and examine it microscopically in 

 water. 



a, The cuticular lining has a very strong spiral 

 thickening, which gives great elasticity to the 

 tube. 



M2 



