i MOVEMENTS AXD GROWTH 7 



alike in this respect. The large dark 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 

 hand, 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 ; it is not present 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 po\ver 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 body, 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 and sharp observation to 

 see a frog feed. It lives upon insects, worms, slugs, and 



