74 Elementary Zoology. 



the lower vertebrates. It is seen in other Amphibia, in many 

 fishes, and in reptiles, the chameleon being the most familiar 

 instance of the latter. 



The body of the frog is moist, the skin secreting a fluid by 

 means of certain glands imbedded therein. A too dry atmo- 

 sphere is ultimately fatal to the animal. 



The body is divisible into head, trunk, and limbs, to which 

 regions of the skeleton (p. 85) correspond. There is no recog- 

 nisable neck or tail. The large motith is provided with teeth, 

 which are limited to the upper jaw. Posteriorly there is but 

 one aperture, the cloacal. On the head are the three organs of 

 special sense ; the nostrils anteriorly, the eyes following, and 

 behind these, on either side, a tight drum-like membrane, the 

 tympanum, which covers the tube leading to the ear. The 

 sense organs, it will be seen, are arranged in a segmented 

 fashion. 



There are some other characters which can be noted with- 

 out dissection. If the mouth be opened, two small orifices, 

 the internal nares, are seen to communicate with the external 

 nares (the nostrils). Considerably further back are the two 

 Eustachian tubes, which communicate with the auditory meatus 

 lying beneath the tympanum. The teeth have been already 

 referred to. The tongue, which is bifid at the tip, and can be 

 stretched to a fair length, is attached anteriorly in the mouth 

 cavity. It is by the rapid extension of the tongue, and by the 

 viscid fluid secreted from it and covering it, that the frog is 

 enabled to capture its (generally insect) prey. 



When the skin is removed preparatory to opening the body, 

 it will be seen to be loosely attached to the underlying muscles. 

 This is caused by the presence of large subcutaneous lymph 

 spaces. When the thin layer of muscles in the abdominal 

 region is cut through, a large cavity is exposed, in which lie 

 nearly all the viscera. This is the body cavity, or cxlom. It 

 extends through the abdominal and thoracic regions, but does 

 not push its way into the head or the limbs. Thus the body 

 of the frog is hollow, the walls consisting of the skin externally 

 and of the skeleton and muscles next, which form together the 

 body-wall. A more careful examination of the ccelom shows 



