AMPHIBIA. 379 



extended works. If possible the cleaving eggs should be 

 studied. 



401. Special Exercises. Describe the life history and the 

 stages in the metamorphosis of the frog. (Fig. 187.) What 

 larval organs disappear? What new organs are introduced? 

 Compare other amphibians as to the degree and facts of meta- 

 morphosis. 



402. Classification of Amphibia. 



Order I. Urodela. Amphibia with tails persistent throughout life ; body 

 elongated; usually two pairs of appendages (sometimes only the anterior 

 are present), which may be poorly developed. 



The principal suborders are : 



1. Perennibranchiata, in which the gills persist throughout life (Nec- 

 turus or water-dog, Siren or mud-eel, and certain blind forms found in 

 caves). 



2. Derotremata. losing the gills in the adult but retaining a spiracular 

 opening in the side of the neck which represents the gill-slit. (Examples: 

 " Congo-snake " of the gulf states, giant salamander of Japan.) 



3. Myctodera, which lose all traces of water-breathing. (Examples: 

 Newts, salamanders, etc.) 



Order II. Anura. Amphibia in which the tail is absorbed in the adult 

 condition, if present in the embryo. Two pairs of appendages, the posterior 

 of which are well developed. Undergo a metamorphosis in which the 

 larvae usually have the " tadpole " form, with gills and tail but without 

 appendages. All traces of gills lost in the adult. The Anura embrace the 

 Bufonidae or common toads, the Ranidae or common frogs, the Hylidae or 

 tree-toads, and other less common families. The Anura include the ma- 

 jority of the species of Amphibia. 



Order III. Gymnophiona. Amphibia with neither legs nor tail; body 

 worm-like ; no gills nor gill-slits in the adult ; eyes more or less degenerate. 

 Scales are present in the skin. Represented by the so-called blind-worms 

 of tropical countries. 



