VERTEBRATA: AMPHIBIA. 517 



As ordinarily known in its native country, the Axolotl is cer- 

 tainly perennibranchiate, and they breed in this condition 

 freely. There is no doubt, however, that individual specimens 

 may lose their gills, without thereby suffering any apparent 

 change, except it be one of colour. The Axolotl, therefore, is 

 in the singular position of being sometimes " caducibranchiate," 

 whilst it is ordinarily "perennibranchiate."* Nearly allied to 

 the Axolotl is the Menobranchus (fig. 277, C) of North America, 

 in which the branchiae are persistent. Amphiuma (f g. 277, B) 

 and Menopoma, as already remarked, differ from the forms just 

 mentioned in losing the gills when adult, but in retaining the 

 external branchial apertures on the side of the neck. The 

 species of Amphiuma are North American, and have both 

 pairs of limbs, though these are of very small size. 



The species of Menopoma, as now restricted, are also con- 

 fined to the fresh waters of the United States, and likewise 

 possess both pairs of limbs. The Giant-salamanders of Java 

 form the genus Sifboldia or Cryptobranchus, and differ from 

 Menopoma chiefly in the fact that the gill-slits are closed in the 

 adult. They reach a length of several feet, and are the nearest 

 living allies of the extinct Andrias of the Miocene Tertiary. 



In the second section of the Urodela, comprising those forms 

 in which the gills are caducous, and both pairs of limbs are 

 always present, are the Water-salamanders or Tritons, and the 

 Land-salamanders. The Tritons are the only examples of the 

 aquatic Salamanders which occur in Britain, and every one, 

 probably, is acquainted with the common Newt. 



The Water-salamanders or Newts (fig. 281) are distinguished 

 from the terrestrial forms by being furnished with a compressed 

 fish-like tail, and by being strictly oviparous. The larvae are 

 tadpole-like, with external branchiae, which they retain till 

 about the third month. The adult is destitute of gills, and 

 breathes by lungs alone, but the larval tail is retained through- 



* Professor Marsh of New Haven has shown that the Siredon lichenoides 

 of the western States of America, when kept in confinement, loses its gills, 

 and dorsal and caudal fins, whilst it changes much in colour, and under- 

 goes various minor modifications in structure. Its habits, also, become 

 less aquatic, and it becomes apparently absolutely identical with Ambly- 

 stoma mavortium, a Salamandroid. This discovery has thrown consider- 

 able doubt upon the value of the distinction between perennibranchiate 

 and caducibranchiate Amphibians, and has rendered it probable that all 

 the species of Siredon are merely larval Salamanders, as long ago suspected 

 by Cuvier. At the same time, the Axolotls certainly breed freely whilst in 

 possession of their branchiae, and there is as yet no proof that they lose 

 their gills whilst in a state of nature. It is, in fact, still uncertain whether 

 all the species of Siredon are merely larval stages of Amblystonia, or whether 

 all the Amblystomce possess a larval 6Yra&-stage. 



