xl 



In Air. The special surface is generally in the form of 

 inpushings (e. g. Tracheae, Lungs, &c.). 



Examples taxonomically arranged. 



In Water and Air. A combination of the two special struc- 

 tures usually present, or a special arrangement to prevent the 

 gills drying. 



Examples. Crustacea : Birgus latro. 

 Gastropoda : Ampullaria. 

 Pisces : Ceratodus, Amia, &c. 



Many fish habitually swallow air, which yields up its oxygen 

 in exchange for the CO 2 in the blood in the vessels of the ali- 

 mentary canal, thus supplementing the respiration by gills. 



N. 



SOUND-PRODUCING ORGANS. 

 (Including Larynx and Syrinx.) 



Used by animals for signalling their presence, to give warning 

 of danger, and exciting sexual passion. 



Not Larynx or Syrinx. 



Examples. The simplest and least-specialized in each class to 



commence the series. 

 Crustacea. 

 Arachnida. 

 Myriapoda. 

 Insecta. 

 Reptilia. 

 Mammalia. 



Larynx and Syrinx. 

 Examples taxonomically arranged. 



