432 



TEXT-BOOK OF ENTOMOLOGY 



the larva of ^Eschna, reddish brown, this tint being due to a 

 finely granular pigment situated in the peritoneal membrane. 



In their essential structure the tracheae consist 

 of the chitinous intima, which is a continuation 

 of the cuticle of the integument, and of a cellular 

 membrane or outer layer of cells (a continuation 

 of the hypodermis) called the peritoneal mem- 

 brane, or ectotrachea (Figs. 392, 393). 



Leydig discovered that the spiral filaments 

 are not distinct and separate, but intimately con- 

 nected with the inner membrane (intima), and he 

 detected the outer or peritoneal membrane, which 

 Chun afterwards found to be epithelial in its 

 nature, Minot stating that it is a true pavement 

 epithelium. 



Figure 393 represents a longitudinal section of 

 a large trachea of Hydrophilus, showing the 

 peritoneal membrane (ectotrachea, ep) and the 

 intima or endotrachea, divided into the cuticula (cu), with the darker 

 colored inner layer, in which are embedded the dark-colored 

 taenidia (/). 



FIG. 893. Longi- 

 tudinal section of the 

 trachea of Hydrophilus 

 piceus : ep, epithelium ; 

 CM, cuticula ; /, spiral 

 threads. After Minot. 



FlO. 894. Testis of Anabrus, ^io\vinir the ramifications of the trachea'. After Minot. 



Distribution of the tracheae. The distribution of the air-tubes, as 

 Lubbock and also Minot state, depends first upon the shape of the 



