BIRDS. 361 



from a little pit or umbilical depression, at the commencement 

 of the groove on the internal surface of the shaft, an accessory 

 plume {pluma accessoria, hyporracMs NlTZSCii), which in the 

 casuary equals the primary shaft in size, but usually is much 

 smaller than it, but is similarly formed. In the flag-feathers of the 

 wings and the tail-feathers this part is never met with. By tlie quill 

 the featliers are fixed in a tube formed by a duplicature of the skin. 



If the feathers be plucked from a living bird new ones come in 

 their place, and this reproduction occurs also annually at the so- 

 named moult. At the bottom of the canal in which the feathers were 

 fastened, a formative fluid is then secreted anew, which gradually 

 accumulates and is included in a vesicle open below. This vesicle 

 quickly assumes the form of an elongated cone of which the base 

 is turned downwards ; it afterwards perforates the skin as a horny 

 case or sheath, and finally at its point gives passage to the vane of 

 the new feather developed within the case. In proportion as the 

 development of the feather proceeds, the horny case is resolved into 

 small scales and plates and partly falls off by shaking of the 

 feathers, or is removed by the bird when it dresses its feathers with 

 its bill. Some downy feathers, of which the shaft is not fully 

 formed but always remains incomplete, secrete on that account a 

 substance or powder wliich falls from this horny case; feathers of this 

 kind have been long known in the herons, where they occur behind 

 on the back, but they are found also in other birds, in some parrots, 

 for instance, and birds of prey. 



Consequently it is the point of the feather that is first seen. 

 The flag also is the part most early formed in the above-named 

 sheath. Afterwards comes the quill, which at first forms a ring at 

 the base of this sheatli, but is afterwards elongated. Lastly the 

 shaft is produced, which at first consists of two lateral parts, which 

 soon coalesce at the horny plate of the anterior side, but remain 

 longer distinct behind, from whence also the longitudinal groove 

 arises which we have noticed on the posterior surface of the shaft. 

 Finally, the membranes that fill the quill are the remnants of the 

 fluid in which the feather was formed and which has gradually 

 dried up in that closed spaced 



1 On the mode in wliich feathers are produced various observations have been 

 published. In our compressed description we have principally made use of A. Meckel 



