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THE AMERICAN NATURALIST [Vol. XLII 



specimen as dark lines. The sense organs were un- 

 doubtedly located beneath these specialized scales, much 

 as the lateral line organs are protected in some of the 

 fishes. In Xecturus (Fig. 2) the arrangement of the 

 lateral line organs is almost identical with what has just 

 been described for Micrerpeton. I have suggested else- 

 where that this similarity in the lateral line organs of 

 these two forms may be indicative of relationship between 

 the groups to which these forms belong. There is no 

 reason why the type of lateral line should not have been 

 preserved in the amphibians, since we know that in some 

 of the fishes certain types of peculiar lateral line struc- 

 ture have persisted for nearly as great a length of time. 



In the structure of the limb bones and ribs the Branchi- 

 osauria are much like the modern Amphibia in that the 

 bones are formed almost entirely of perichondrium. 

 There are never any bony epiphyses in any of the Am- 

 phibia. In some of the toads Parsons has seen the 

 cartilaginous epiphyses calcified, but they are never 

 osseous. The endochondrium is not at* all or but 

 slightly developed in the Amphibia, and in the fossilized 

 bones this condition causes a concavity at the ends. In 

 the Microsauria the endochondrium is more fully formed, 

 although there are some in which the ends of the limb 

 bones are nearly flat. 



The form of the body in the Branchiosauria is stri- 

 kingly salamandrine, as may be seen by referring to fig- 

 ures 1 and 4. In Micrerpeton the tail is quite long and 

 almost equals the length of the presacral region. In the 

 Branchiosaurus fayoli Thevenin (Fig. 4), the tail is 

 shorter but the form is much the same. The body of the 

 Branchiosaurus (Fig. 4) is more stout than that of the 

 Micrerpeton (Fig. A) and the ribs are longer. 



In summing up all of the characters as presented by 

 the Caudata and the Branchiosauria it seems most prob- 

 able that the Caudata are but degenerate Branchi- 

 osaurians and the changes which have taken place in the 

 skeleton are mostly brought about by the loss of certain 

 parts. 



