274 ZOOLOGY SECT. 



terrestrial animal. At the same time further adaptations to land- 

 life take place, the most important being the modification of the 

 blood-vessels consequent on the disappearance of the gills, the loss 

 of median fins, and the strengthening of the limbs to support 

 the weight of the body. 



External Characters. An excellent example of the lower 

 Urodela with persistent gills is afforded by the great North Ameri- 

 can Water-newt, Necturus macnlatus (Fig. 886 bis). The animal 

 attains a length of 30 cm. (more than a foot) ; the elongated trunk 

 is separated by a slight constriction from the depressed head and 

 passes insensibly into the compressed tail, which is bordered by a 

 continuous median fin unsupported by fin-rays. The limbs are 

 small and weak in proportion to the size of the body, and in 

 the ordinary swimming attitude are directed backwards, more or 

 less parallel to the sagittal plane, the upper arm and thigh 

 taking a direction backwards and slightly upwards, the fore-arm 

 and hand and the shank and foot extending backwards and 

 downwards. Each limb thus presents an external or dorsal and 

 an internal or ventral surface, an anterior ^or pre-axial borHer 

 which terminates in the first digit and a iposterior of post-gxial 

 border which terminates in the last digit. The eyesxare small 

 and have no eyelids, there is no tympanic membrane* and the 

 mouth is wide and bordered by thick lips. On each side of trie 

 neck are two gill-slits (br. cl. 1, br. cl. 2) leading into the ^>tarynx y 

 the first between the first and second branchial arches, th& other 

 between the second and third. From the dorsal end of each of the 

 three branchial arches springs a branched external gill (br. 1 br. 3). 

 Very similar in its external characters is the blind, cave-dwelling 

 Proteus, and Siren (Fig. 887) differs mainly in its elongated eel- 

 like body and in the absence of hind-limbs. All three genera are 

 perennibranckiate or persistent-gilled. 



The remaining Urodela are often called cadu&bmnchiate or 

 deciduous-gilled, and furnish a complete series of transitions 

 from derotrematous forms which, while losing the gills, retain the 

 gill-clefts, to scdamandrine forms in which all trace of branchiate 

 organisation disappears in the adult. In Amphiuma (Fig. 888) the 

 body is eel-like and the limbs are extremely small : there are no gills 

 in the adult, but two pairs of gill openings are retained throughout 

 life. In Cryptobranchus there is a. single branchial aperture, 

 sometimes present on the left side only, but, as in the previously 

 mentioned genera, four branchial arches are retained. In 

 Megalobatrachus, the Giant Salamander of Japan and China, all 

 trace of gill-slits disappears, but two branchial arches persist. 

 Lastly, in the Salamanders, such as the Spotted Salamander ($aAx- 

 mandra maculosa, Fig. 889) of Europe and the common British 

 Newts (Molge), the adult has no trace either of gills or gill-slits, 

 and the branchial arches are much reduced. The limbs, also, in 



