322 



THE BIOLOGY OF THE FROG 



CHAP. 



The skin of the frog is an organ of unusual sensibility. It 

 is sensitive not only to touch, chemical stimuli, and differences 





Fig. 86. — Touch corpuscle of the frog with its supplying nerve. The 

 branches of the nerve may be seen ramifying between the flattened cells 

 of the sense organ. (From Gaupp, after Merkel.) 



of temperature, but it is affected in no small degree by 

 light. It is also readily influenced by changes in the mois- 

 ture of the air, as is indicated by the behavior of the animal 

 under different conditions of the atmosphere. 



Sense Organs of the Mouth. — In the mouth there are in 

 addition to the nerve endings in the general epithelium 

 numerous sense organs which have been supposed to be 

 concerned with the sense of taste. They occur on the 

 flattened surfaces of the fungiform papiliae of the tongue and 

 also on the floor and roof of the mouth, where they assume 

 a more rounded form although possessing essentially the 

 same structure in both regions (Bethe). The surface of 

 these organs is covered by cylindrical epithelial cells between 

 which are scattered various forms of elongated cells which 



