THE PHYLA ARTHROPODA AND ONYCHOPHORA 



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Fig. 15.38. A, Chilopoda: a large tropical centipede. Note the poison 

 fane;s attached to the posterior end of the head; each contains in its base 

 a sfland, the toxic secretion of which passes throu8;h a duct to a minute 

 pore near the tip of the fang. B, Diplopoda: a milHpede, Spiroboliis. 

 There are two pairs of appendages for each division of the body, with the 

 exception of a few just behind the head. Each division represents the 

 product of fusion between two adjacent somites. {A, photograph courtesy 

 New Yort: Zoological Societv; B, photograph by Charles W. Schwartz.) 



mouth parts and sense organs, the tracheal respiratory system with segmental 

 spiracles, and the exoskeleton which must be molted to permit growth. Al- 

 together, chilopods and diplopods present an interesting mixture of annelid- 

 like and insect-like features, in addition to adaptive characteristics peculiar 

 to their kinds. This has led to the supposition that their ancestors developed 

 from an evolutionary stock of terrestrial mandibulate arthropods rather early 

 in its history, and that they demonstrate the capacity of this stock to evolve 

 features which were later perfected in the Insecta. 



479 



