94 HIGH SCHOOL ZOOLOGY. 



spiracle of the sharks and Ganoids, and is closely related to the 

 internal ear even in tliese forms. A columella longer than that 

 in the Menobranch stretches between the tympanic membrane 

 and the fenestra ovalis. 



20. As regards the intestinal appai*atus, the Aniira pre- 

 sent many differences from the Urodeles. The tongue, which 

 is little developed in the latter, becomes in the foi-mer the 

 chief organ for securing the insects on which they feed, as it 

 is free behind and can be shot out with great rapidity. It 

 is only absent in two tropical foi-ms, Aglossa. The males of 

 some species are furnished with air-sacs, which serve as resona- 

 tors to reinforce the sounds })roduced by the larynx, which is 

 better developed than in the Menobranch. Although the adult 

 Anura are carnivorous and the-ir intestine is comparatively 

 short, yet the larvaj or tadpoles have a very long coiled-up 

 intestine. They are omnivorous, but chiefly live on vegetable 

 substances which they gnaw with their temporary horny jaws. 



21. It will be at once i*ealized that the metamorphosis 

 of the Anura brings about greater changes both in the form *of 

 the body and the habits of life than in the Urodeles. The 

 period of development at which it occurs may be very different, 

 the tadpole phase being sometimes very brief and in other cases 

 much longer. It may in certain cases be retarded by external 

 conditions where it ordinarily occurs early. Most of the forms 

 lay their eggs in water, surrounded by a quantity of gelatinous 

 substance forming the frog's s[)awn, but othei- forms which have 

 not free access to water, adopt other plans. In one of the 

 Aglossa for instance, the Surinam toad — Pipa (Fig. 69), the 

 eggs are placed in enlarged cutaneous glands on the back of the 

 mothei", where they are hatched out and pass through their tad- 

 pole-phase. The common toad, again, requires only very small 

 pools in which the lai-vse pass their short aquatic life. 



