46 AMPHIBIA 



CHAP. 



The same kind of organs occur in Amblystoma. 1 They appear, 

 previous to the breaking open of the gill-clefts, as protrusions of 

 epiblast, long before any of the external gills on the branchial 

 arches. When the clefts have broken open, the quadrate sends 

 out laterally a tiny crescent-shaped process a little above the jaw- 

 joint, and this process extends to the base of the balancer, but 

 not into it, and a bundle of muscle-cells grows into the balancer. 

 It is easy to recognise the same organ in the extremely long 

 thread-like structures of the larva of Xenopus. In the Apoda 

 they are likewise present, but are retained permanently as highly 

 specialised, probably tentacular organs (cf. p. 86, Apoda). 



One of the most unexpected features is the suppression of 

 the lungs in various kinds of Salamandridae. The lungs are 

 either reduced to useless vestiges or they are quite absent. This 

 occurs in aquatic and terrestrial, American and European forms, 

 and it is noteworthy that the reduction of the lungs does not 

 apply to all the species of the various genera, nor is it restricted 

 to one sub-family. 



The following list is due to the researches of H. H. Wilder, 2 

 L. Camerano, 3 E. Lonnberg, 4 and G. S. Hopkins 5 : All the 

 Desmognathinae and Plethodontinae ; Amblystomatinae, Ambly- 

 stoma opacum ; Salamandrinae, Salamandrina perspicillata. In 

 Triton and other Salamandrinae the length of the lungs varies ; 

 in some they extend more, in others less, than half way down the 

 distance between head and pelvis. Hopkins remarks : " Two 

 questions are naturally suggested by this apparently aberrant 

 condition of the respiratory organs. First, what structures or 

 organs have taken on the function of the lungs and branchiae ; 

 and secondly, is there any modification in the form or structure 

 of the heart which in any way may be .correlated \vith the above- 

 mentioned peculiarities of the lungless forms ? " Wilder con- 

 cluded that respiration was probably carried on by the skin, and 

 perhaps, to some extent, by the mucosa of the intestine. Camerano 

 thinks that, at least in the European forms, respiration is effected 

 by the bucco-pharyngeal cavity, and that the skin affords no 

 efficient aid. The left auricle in the lungless forms is much 



1 Orr, Quart. J. Micr. Sci. xxix. 1889, p. 316. 



2 "Lungenlose Salamandriden," Anat. Anz. 1894, p. 676 ; 1896, p. 182. 



3 " Nuove ricerche anatomo-fisiologiche intorno ai Salarnandridi iiormalmente 

 apneumoni." Torino, 1894. 



4 Zool. Anz. 1896, p. 33 ; 1899, p. 545. 5 Amcr. Natural, xxx. 1886, p. 829. 



