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MANUAL OF ZOOLOGY 



/us. Appended to the chyle stomach at its anterior end are 

 in many insects a number of tubular pouches, the hepatic 

 caeca {axe). At the junction of the chyle stomach with the 

 small intestine, or further back, there open a number (from 

 2 to over 100) of narrow tubular appendages, the Mal- 

 pighian tubes (map), which are the organs of renal ex- 

 cretion. The intestine is usually 

 elongated, its posterior portion is 

 dilated to form a wide rectum, 

 which opens in the anal aperture 

 on the last segment. Anal glands 

 producing an odoriferous secretion 

 often open into the rectum. 



The organs of respiration are a sys- 

 tem of fine branching tubes, the tra- 

 chea (Fig. 147), which communicate 

 with the exterior through valvular 

 apertures known as stigmata situated 

 at the sides of the segments. These 

 tracheae form a completely ramify- 

 ing system which conveys the air to 

 all the parts of the body. The wall 

 of the tubes is strengthened by a 

 series of spirally wound chitinous 

 fibres, each fibre or thread making 

 from one to four or five turns around 

 the trachea?. In some insects, mainly 

 those adapted for active flight, the tracheal system is dilated 

 in certain parts of the body to form large air sacs. In the 

 aquatic larva? of some insects there is a series of soft external 

 simple or divided processes ■ — the tracheal gills — attached 

 to the abdominal segments, and richly supplied with trachea? 

 which have no communication with the exterior. 



Fig. 147. — Periplaneta. View 

 of the arrangement of the 

 principal trunks of the tracheal 

 system. (After Miall and 

 TJenny.) ' 



