I MOVEMENTS AND GROWTH 7 



large black patch situated behind the eye and containing the 

 tympanic membrane, is, however, always present, and is one 

 of the chief distinguishing marks of the common British frog 

 as compared with other kinds, such as the " edible frog" of 

 the Continent. 



Sexual Characters. — As in so many of the more familiar 

 animals there are two sexes of frogs, easily distinguished 

 from one another. If you examine several of them you will 

 find that a certain number have on the palm of the har^^, 

 towards the inner side, a large swelling, rather like the 

 ball of our own thumb, but much more prominent and of 

 a black colour. Frogs having this structure are males ; 

 there is no trace of it in the females. 



Actions performed by the Living Frog.— Kept under 

 suitable conditions a frog very soon shows evidences of life. 

 If touched or otherwise alarmed it attempts to escape by 

 making a series of vigorous leaps — suddenly extending the 

 hind-legs and jumping to a considerable height. Thrown 

 into water it swims by powerful strokes of the hind-limbs. 

 It has thus, like so many living things with which we are 

 familiar, the power of voluntary movement. 



If kept under observation for a sufficient time — weeks or 

 months — it will be found that frogs grow until they reach a 

 certain limit of size. Growth, in the case of the frog, is an 

 increase in size and weight affecting all parts of the b9dy, so 

 that the proportions remain practically unaltered, and no 

 new parts are added. 



Careful observation shows that the throat is constantly 

 rising and falling, and the nostrils opening and shutting. 

 These movements, like the expansion and contraction of 

 the human chest, are respiratory or breathing movements, 

 and serve to pump air into and out of the lungs. 



It requires frequent watching arid, sharp observation to see 



