ME. E. DEGEN ON ECDTSIS. 377 



individuals which I have examined. Whenever I met with any exception it happened 

 only where the remex in moult had been accidentally retarded in growth. The latter 

 case can invariably be detected from the normal course of development which the 

 major covert pursues, provided that the anomaly has not been caused by external 

 injury. 



Now and then the allied covert is shed a little in advance of its remex, but in the 

 majority of individuals it is shed simultaneously with it. Only in three cases did I 

 find the conditions reversed — that is, the remex preceding the principal dorsal covert 

 in moult by being shed first. 



The rule therefore of the dorsal major coverts slightly preceding in moult their 

 respectively accompanying flight-feathers is a character inherent to the conditions 

 prevailing for the acquisition of the first or plumage of the fledgling bird. 



This law being so uniformly carried out as regards the metacarpo-digital portion, a 

 few remarks, having reference to the alleged undecem-pennate forms of Passerine birds 

 of Gadow (21), may be made here. 



So long as it was taken for granted generally that the main covert directly asso- 

 ciated with a quill was the one which lies proximad to the latter, it follows that 

 Dr. Gadow was without question fully entitled to the conclusions he had then 

 arrived at in regard to the exact relationship of the terminal feathers. But, when 

 inquiring later into this matter (Degen (16), pp. x-xiii), I was able to show histo- 

 logically, as well as by means of the physiological conditions of moult (see also 

 figures 2 «& 3, I. c), that the conditions were invariably reversed, viz., that the major 

 coverts most intimately connected with the main quills were those which are lying clistad 

 to the latter. This naturally had the efi'ect of leaving one feather less to be disposed 

 of, instead of the two supernumerary ones as in the case of Dr. Gadow (his alleged 

 11th quill and its corresponding covert), for a great number of genera and species of 

 Passeres; those with 9 and those with 10 primaries alike, including amongst the 

 latter also the species under special consideration. Dr. Gadow's own words (pp. 659 

 & 660, I. c.) on this point are : — " In some cases there might be some doubt whether 

 the little terminal feather in question is really a primary, but this can easily be 

 settled by the presence of the corresponding upper coverts. Moreover, there are many 

 cases in tvhich the primary is still longer than its covert ^. When the 10th or 11th 

 quill is much shortened, the corresiionding lower covert is absent in the Passeres ^. The 

 Alaudidce prove that the 10th quill is capable of being shifted dorsalwards, so that 

 it becomes enclosed between the outer vane of the 9th primary and the 10th upper 

 covert, instead of being freely visible below and in front of the 9th primary ; when seen 

 from below, it is hidden by the outer vane of the 9th primary. This shifting explains 

 the conditions which are the rule amongst the birds of Group D (p. 664, I. c). The 

 11th primary undergoes a similar dislocation in a more marked degree " ^ 



' These italics are mine. 



