2i6 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



Reptiles. — As a class these are silent, although a few 

 do make sounds intended as calls. 



In amphibians, however, especially in frogs, we have 

 again animals abundantly vocal. Their vocal organs are 

 indeed very imperfect, but their 

 lungs, which are hollow sacs 

 capable of great distention, act 

 as powerful resonant cavities, 

 giving considerable volume to 

 their voice. 



Fishes, being gill-breathers or 

 water-breathers, can have no 



voice in a proper sense. Probably some of them do 

 make audible sounds, but not vocal. 



Arthropods ; Insects. — True voice is confined to air- 

 breathing vertebrates, and is connected with respiratory 



passages ; but if we extend 

 the term to any sounds 

 intended to be heard by 

 mates, then we may include 



Fig. 138. — Transverse section 

 just above the bronchi : vc, 

 vocal cords. 



Fig. 139. — A, sonant organ of an orthopter : rm, resonating membrane : 

 r, rasp. B, the same, magnified. 



insects also among natural musicians. If birds are the 

 vocalists, then are insects the instrumentalists of Nature. 



