Mr W. Macgillivray on the Covering of Birds. 125 



cristatus are not more than a quarter of an inch in length, while 

 some of the posterior dorsal exceed two feet. Even in the same 

 part of two species of the same genus, the greatest difference is 

 often observable in this respect. Compare, ibr example, the 

 scapulars of Ardea cinerea and Ardea garzetta. 



Besides the feathers properly so called, there enters into the 

 constitution of the plumage or general envelope, another modifi- 

 cation of the same general nature. On removing the whole of 

 the feathers whose tips appear externally, in certain orders, and 

 especially in the aquatic birds, we find the skin still covered 

 with a more or less dense envelope of a very soft, filamentous, 

 highly flexible, and very elastic substance. This is the down^ 

 tomenturriy diivef. It also consists of individual parts, for which 

 we have no general name in our language, nor indeed in any 

 other that I am acquainted with. The name which seems most 

 applicable to this sort of feather is plumule. 



A plumule, plumula, plumule, consists of two parts ; a small 

 tube, less perfect in form and texture than in the feather, being 

 very narrow, soft, and not well defined in its lower or proximal 

 part, and having its walls composed rather of soft scales than of 

 one continuous piece ; and a pencil of filaments issuing from 

 the base of this tube internally, without any connecting shaft. 

 These filaments vary in length and number, according to the spe- 

 cies. In all cases they are extremely slender, pliant, sinuous, 

 and more or less spirally twisted. They consist of an extreme- 

 ly delicate shaft, along the sides of which there come off, in ge- 

 neral, two sets of short delicate filaments. The former may be 

 denominated the filaments, the latter the filamentules, corres- 

 ponding to the barbs and barbules of the feather. These fila- 

 mentules have the same relation to the filament, their shaft, that 

 the barbules of the feathers have to their barb, and are, in ge- 

 neral, equally distichous ; but they enter into no connection, re- 

 maining perfectly loose, and, owing to the manner in which the 

 shafts are twisted, have the appearance of coming off all round 

 them. The general arrangement, as has been observed, is in 

 two rows ; in the down of Sula alba it is in three, one row con- 

 sisting of filamentules somewhat shorter than the others, and di- 

 rected toward the end of the filament. The filamentules of 



