226 AMPHIBIA 



function is performed by the buccal cavity and pharynx. In 

 Autodax lugubris, a lungless species which is common in 

 California and which never enters the water, the throat vibrates 

 rapidly, from 120 to 180 times per minute, drawing in and send- 

 ing out air ; since a frog breathes by forcing air into its lungs, 

 raising the floor of the mouth while the external nostrils are 

 closed, it is easy to understand that the same action carried on 

 with the nostrils open would only drive air in and out of the 

 mouth. In this case the lungs would no longer be used and 

 would therefore in the course of evolution diminish and at last 

 disappear or become vestigial and functionless. We see then 

 that the loss of the lungs may have been caused by a very 

 slight change in the respiratory movement. In Spelerpes por- 

 phyriticus, which lives in the Alleghany mountains of North 

 America, Dr. Gadow found that the respiration by movements 

 of the throat was very limited, most of the oxygen required being 

 absorbed through the skin which is very moist and slimy. This 

 species is found only in wet places and is very sensitive to 

 drought ; when the skin becomes dry the animals show signs 

 of suffocation and great discomfort. 



The respiratory adaptations in the larvae especially in those 

 whose development takes place within the egg, not in the free 

 state, are remarkably varied and interesting ; the most import- 

 ant are described in the section dealing with breeding habits 

 and development. It is curious to compare the various modes 

 in which the larval stage is modified in Amphibia with the em- 

 bryonic adaptations of reptiles, birds and mammals. In all 

 these three classes the embryo is always provided with oxygen 

 by means of the allantois, which is an outgrowth of the hind-gut. 

 The Amphibia, on the other hand, although they possess in the 

 urinary bladder which opens into the cloaca an organ answering 

 to the allantois of the embryos of higher vertebrates, make no use 

 of this structure as a respiratory organ. In the Californian newt, 

 Autodax lugubris, in which the whole of the metamorphosis takes 

 place within the egg, the external gills, instead of being branched 

 or fringed, form on each side a broad three-lobed membrane of 

 which the outer surface is applied to the inner surface of the egg- 

 capsule, in this respect resembling the allantois of the higher 

 classes. In Plethodon cinereus, on the other hand, in which also 

 the gilled stage is passed within the gelatinous capsule of the egg, 



