2-54 STRUCTURE AND CLASSIFICATION OF BIRDS 



111 which it is present or absent. When present it is in- 

 variably tufted, and generally of fair size. In Cacatua sul- 

 l>1tiirca, however, the oil gland, though present, is small, and 

 has but a single small down feather upon it. 



The parrots are a group of birds which agree with the 

 Accipitres in that some genera have powder-down patches 

 while others have not. The table already referred to indi- 

 cates the facts so far as they have been ascertained. The 

 degree of development of the powder-downs, however, differs 

 considerably, though in no parrot is there more than a single 

 pair of definite powder-downs which are lumbar in position. 

 In Cacatua sulplmrea, for instance, there are a pair of such 

 patches, one on either side of the dorsal tract. These send 

 up a few scattered powder-down feathers as far forward as 

 the neck, and a few to carinal spaces and between the 

 branches of the ventral tract. 



In Calopsitta Novte Hollan,dicc there are the same lumbar 

 patches of a reniform outline ; but the powder-downs are 

 entirely confined to this region of the body. 



Calyptorhynchus stellatiis is more like Cacatua, but the 

 lumbar patch is not so well developed. 



In Psittacula passerina there are lumbar patches more 

 elongated but narrower than those of the parrots already 

 referred to ; there are also scattered powder-downs not 

 aggregated into patches. 



Brotogerys tirica has no defined patches, but simply a 

 few scattered powder-downs, which, however, are more nume- 

 rous in the lumbar regions. In Coracopsis, Chrysotis, and 

 Pionits there are the same generally diffused powder-down 

 feathers not aggregated into definite tracts. The same may 

 be said generally of Psittacus, though such powder-downs as 

 there are are limited to the lumbar region. 



The general pterylosis of the parrots is as follows : From 

 the general covering of the head arises a narrow dorsal tract, 

 which bifurcates in the interscapular region. Between the 

 arms of this fork are the arms of another fork, which unite 

 near the oil gland to form the single straight, short posterior 

 part of the dorsal tract. On the ventral surface the tract is 



