368 H. D. REED 



deles grouped here exhibit unmistakably the impression of ter- 

 restrial existence upon the sound-transmitting apparatus. The 

 state of these organs in Salamandra is a parallel for that in the 

 Amblystomidae, although a bit more inclined toward the terres- 

 trial type. The Tritons, Diemictylus, and Siren, whatever their 

 present-day habits, possess a type of sound-transmitting organ 

 that could have become perfected only in the terrestrial zone. 

 The columella has been a functionless structure for such a con- 

 tinued period that, in recent forms, it fails to produce a stylus or 

 a permanent communication with the suspensorium, and at a 

 very early period of development is effaced completely through 

 fusion with the ear capsule, leaving the operculum only to com- 

 municate with the exterior through the M. opercularis and the 

 arm. Diemictylus and Siren have returned to an aquatic abode 

 so recently as still to retain the sound-transmitting apparatus in 

 its former highly specialized state. They are, therefore, con- 

 sidered as having departed in this respect most widely from prim- 

 itive conditions, and accordingly represent the culminating 

 branches of the amblystomid stem or legion. 



Legion II, the plethodontid group. The arrangement of this 

 group is not fraught with as many difficulties as the former, since 

 the morphological nature of the sound-transmitting organs is 

 such that the generalized and specialized states are easily de- 

 tected. This minimizes the difficulties of phyletic arrangement. 



The distinctive peculiarities of the sound-transmitting appa- 

 ratus of this legion are found in the presence of a single, but com- 

 pound, fenestral element under all conditions of life and at all 

 stages of development. The stylus is always present and is con- 

 nected with the suspensorium. The variable element is the M. 

 opercularis, which is present or absent, accordingly as the animal 

 is terrestrial or aquatic in habit. The state of this muscle is 

 precisely that which obtains among the forms of legion I. In 

 the amblystomid legion the two elements, columella and oper- 

 culum, are always distinct so far as fusions between them are 

 concerned. In legion II, or that which is conveniently termed 

 the plethodontid group, representatives of the columella and 

 operculum fuse with each other in varying degrees, resulting in 



