72 THE SENSES OF ANIMALS 



mentioned briefly, have voices which may be croaks, grunts, 

 trills and even bell-like notes. Newts are voiceless; and the 

 reason for this may puzzle a student who has not given 

 attention to the matter. It is during the breeding season that 

 the sounds made by frogs and toads are most frequent and 

 noticeable. This is because the croaking of the males and 

 the feeble answering calls made by the females help to keep 

 a colony together in order that mating and fertilization may 

 be completed satisfactorily. These sounds may also be re- 

 garded as a form of vocal display and in some species defence 

 of territory. Newts, on the other hand, are not colonial in 

 their spawning, and there is quite an elaborate courtship in 

 most species which takes the form of active movements by 

 the males which curve their tails, show off their seasonal 

 bright colours — mostly on the belly — and nudge and push 

 the desired females in order to stimulate both them and the 

 males as well. This kind of display is mainly visual, though 

 touch plays its part. It is therefore not surprising that newts 

 make no sounds and do not possess vocal cords. This being 

 so they have no need for hearing. The squeaks which emerge 

 from newts which are carelessly handled are mechanical, and 

 are caused by the air from within their bodies being forced 

 out. 



The reptiles vary very much in regard to sound. Snakes 

 have no ears but they are very sensitive to vibrations from 

 the ground. The receptive mechanism to deal with this will 

 be fully referred to in Part II. Tortoises and terrapins can 

 hear well, though the sounds they utter are largely limited to 

 various kinds of hissing. Crocodiles and alligators can roar 

 quite loudly but they have watertight ear-flaps which, how- 

 ever, do not stick out from the head. They can hear sounds 

 both in water and on land. 



The lizards have very sensitive ears, though here again 

 there are no external ear-flaps. The sounds made by some 

 lizards are confined to hisses which in some species are almost 

 loud enough and low enough in pitch to be designated 

 "roars". Sound plays little part in the courtship of lizards 

 which is mainly of a physically demonstrative nature ; but 

 their hearing is much used when hunting prey. Even our 

 own three lizards — the Common or Viviparous Lizard, the 



