INVERTEBRATE ZOOLOGY. 49 



lateral raj-s. Median fin continuons 

 around tail. Swimming-bladder func- 

 tions as Inng. Grills with operculum. 

 In one species small external gills. A 

 very small, but isolated group, including 

 3-4 species. These represent two orders. 



Order 1. Monopneumones Lung (=swimming-bladder) single. 



ir Ceratodus. 



Order 2. Dipneumones A pair of lungs present, -ji; Protopterus. 



Class III. Amphibia Skin naked, very glandular and slimy. 



Grills, external and internal, present at 

 some stage, generally transitory. Lungs 

 usually present, with larj'nx and trachea. 

 Paired limbs of the hand-form {cheirop- 

 terygium) with normallj' five digits, often 

 reduced in immber. Two occipital con- 

 dyles. 



Order 1. Urodela Body elongated. Tail persistent. 



Sub-order 1. PereiDiibnoicJikifa. .. .With external gill-bushes and me- 

 dian fin in caudal region. -^ Necturus. 



Sub-order 2. Derotremata No external gills, but with a persistent 



gill-slit, -if Menopoma. 



Sub-order 3. SalanuDidridii . .. .External gills and gill-slits embryonic or 



larval. Adult breathe by lungs, or by 

 pharyngeal and integumental respira- 

 tion, the lungs failing. 

 •^ Salamandra, Desmognathns. 



Order 2. Gymnophiona Serpentine subterranean forms without 



tail, limbs or gills. Integiiment with 

 minute scales sunken in pits. -^ Coecilla. 



Order;!. Anoura Compact, cephalized forms, with tail 



present only in larval life. Hind legs 

 enormously developed and used for leap- 

 ing and swnmming. No gills when adult. 

 ii^Rana, Bufo. 



