{46}The same kind of organs occur in _Amblystoma_.[18] 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,[19] L. Camerano,[20] E. Lönnberg,[21] and G. S. Hopkins[22]:–All the Desmognathinae and Plethodontinae; Amblystomatinae, _Amblystoma 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 with the above-mentioned peculiarities of the lungless forms?" Wilder concluded 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 {47}smaller in comparison than the right, and there is no pulmonary vein. The auricular septum has a large aperture, the communication between the auricles being larger than even in _Necturus_ (which breathes essentially by gills). The sinus venosus, instead of opening into the right auricle only, opens more freely into the left than into the right, and the latter communicates more directly with the ventricle than the left, instead of about equally. In short, the heart of these creatures appears almost bilocular, instead of being trilocular, at least functionally.