1883.] 203 [Jeffries. 



and there could be no doubt that the change was due to the action 

 of the elements. Many observations were made regarding the 

 induration of these sandstones, which are not here given, but all 

 tended in the same direction — to show that atmospheric agencies 

 exercised a strong indurating influence upon the surface and 

 immediately underlying portions. 



THE EPIDERMAL SYSTEM OF BIRDS. 



BY J. AMORT JEFFRIES. 



The epiderm of birds possesses a much larger variety of appen- 

 dages than that of any other vertebrate group. These appendages 

 have, from time to time, been compared in various ways to the 

 epidermal appendages found in the other groups; and of late 

 years an effort has been made to show the direct homology of 

 feathers, hairs and scales. Indeed this has gone so far that all 

 the epidermal appendages have been reduced by some to one 

 type. 



To investigate these homologies and to compare the varying 

 products of the epiderm of birds with those of the other groups 

 are the objects of this study. The structure of feathers, scutae, 

 claws, spurs, toe-pads, bills, combs, wattles, and spines of the 

 tongue and mouth, have all been studied as found in the adult, 

 and their development has been followed from the third day of 

 incubation. As much has already been writen on the structure 

 of feathers any description of their adult form is omitted in this 

 paper. 



My embryological studies have been made for the most part 

 on the chick and duckling, yet many forms of the other orders 

 have been examined. In all cases they have been found the 

 same, so that any statement made for the chick may in all proba- 

 bility be extended to cover the entire group of carinate birds. 



A word as to the method or order of this article. First, the 

 naked skin is considered, and then one after another of its 

 products. In each of these separate subjects the literature is 

 first considered, then the adult structure, and then its develop- 

 ment. All questions of morphology and the like are deferred to 

 the end, where they are discussed in the light cast upon them 

 by the previous descriptions. 



