METHODS OF DEGENERATION IN THE OSTRICH. 



By Prof. J. E. DUERDEN, M.Sc, Ph.D., 



Professor of Zoology, Rhodes University College, Orahamstown ; Officer- 

 in-Charge, Ostrich Investigations, Grootfontein School of Agriculture, 

 Middelhurg, G. P., South Africa. 



(With Plates V and VI, and 8 Text-figures.) 

 CONTENTS. 



PAOE 



Introduction 131 



Under-coverts : First Row ; Second and Third Rows . 135 



Upper-coverts 141 



Remiges or Wing Quills 144 



Leg Coverts 151 



Bald Head Patch 153 



Down 155 



Digits of the Wing : Plumes on Third Finger . . 157 



Fourth Outer Toe and Claw . 162 



Scutellation of Middle Toe 169 



Degeneration and Adaptation ...... 177 



Ontogenetic and Phylogenetic Degeneration . . . 180 



Cause of Degeneration ....... 184 



Factorial Changes 187 



The Ratitae or running birds, as qontrasted with the Carinatae or 

 flying birds, have long been regarded as a degenerate group. A loss of 

 structural parts has taken place in various directions, yet on somewhat 

 similar lines throughout, pointing to some retrogressive influence common 

 to all the representatives of the sub-class. The loss of effective barbicels, 

 leaving the vane of the feather loose and open and incapable of offering 

 resistance to the air, has rendered flight impossible^ Probably as a 

 result of the same degenerative tendency, other losses of plumage 

 have taken place, as well as a total loss or reduction in the size of the 



1 The barbicels have almost disappeared in Struthio but are much better developed in 

 Rhea. Chandler in his paper, "A study of the Structure of Feathers," gives illustrations 

 of the two on Plate 18, Univ. Calif. Publ. Zool. Vol. xiii. 1916. 



