VOL. xin.] DOWxN TRACTS IN NESTLING BIRDS. 79 



an ordinary passerine species. This fact, coupled with what 

 appears to be a rather misleading name, prompts me to make 

 the following suggestions. 



Instead of" inner " and " outer supra-orbital tracts," more 

 distinctive terms would be " capital tract " for the former 

 and " supra-orbital tract " for the latter. My reasons for 

 coming to this conclusion are these : — 



i. In the majority of newly-hatched passerine birds 

 (i.e., Motacilla a. lugubris, Parus major, Turdus viscivorus) 

 the forward ends of the so-called " inner supra-orbital 

 tracts " spring from points much nearer the centre of the 

 crown than the lids of the closed eyes. These tracts then 

 run in diverging lines along either side of the head (c/. 

 accompanying figures). 



ii. The so-called "outer supra-orbital tracts" are very 

 frequently wanting ; consequently the comparative term 

 "inner" is usually unnecessary and, therefore, misleading. 

 While on this subject I would like to draw attention briefly 

 to the marked difference between the nestling Rook (C. 

 frugilegus) and that of the Carrion-Crow (C. corone). As 

 may be seen in the accompanying figure, the latter is relatively 

 well supplied with down. This is smoky- or greyish-white 

 in colour and matches fairly well the " under down " of the 

 adult bird. When newly-hatched the skin of the body is a 

 deep yellowish flesh-colour and only acquires the blackish 

 tinge after about the fourth day. The inside of the mouth 

 changes from dull orange-yellow at hatching to a reddish- 

 yellow during the first twenty-four hours, and later (by about 

 the third day) to a rich carmine or purplish red.* 



In the Rook the down is more scanty and of a dark smoke- 

 grey colour. It is completely absent from the head, while 

 the humeral and spinal tracts are noticeably abbreviated. 

 The skin and inside of the mouth are also much darker 

 immediately after hatching than in the Carrion-Crow. 



* The adult has the tongue and roof of the mouth blackish. 



