1883.] 217 [Jeffries. 



that the sheath takes part in the formation of the quill ; this is 

 an error, it simply remains in contact with the quill since it is 

 held there by the skin. 



I have not been able to secure satisfactory pin-feathers in 

 which to study the formation of after-shafts. Studer, however, 

 has shown that they are formed in the same manner as the main 

 shaft but opposite to it. 



As the tip of the feather becomes complete, long before the 

 quill is begun, the feather sheath dries up and is rubbed off by 

 friction, thus allowing the feather to unfold and set in its proper 

 form. This gives the appearance of the feather being pushed 

 out through the sheath as stated by the old authors. Samuel, to 

 disprove this, cut all the nerves of a pigeon's wing, thus paraliz- 

 ingit and then plucked out some of the primaries. The feathers 

 which grew to replace those plucked out retained their sheaths 

 since there was no friction. Much the same thing may be seen 

 in nestlings. 



The pulp dries up at the tip as the feather becomes formed and 

 leaves only a light cuticular film, the pith of the quill ; most of 

 the substance of the pulp is absorbed. 



Pigment when present is simply formed inside the cells of the 

 feather, and is often different from the color given off by the 

 feather. 



To sum up : First, the feathers of adult birds are developed on 

 the same plan as the down-feathers, — by a renewed growth of the 

 primitive papillae ; yet in the formation of the feather the condi- 

 tions found in down-feathers are never present. Secondly, the 

 same distinctions can be introduced as into the epiderm of the 

 embryo. Thirdly, the under surface of the vane and shaft is the 

 inner surface of the epiderm, which in all other cases in the verte- 

 brates is in connection with the cutis vera. Finally, the cutis 

 vera is exposed to the air at the umbilicus; or, more accurately, 

 would be exposed were it not for the cellular films which form 

 the pith of the quill, left by the retreating pulp. 



SCUTAE. 



The scutae, or scales, on the tarsi of birds are folds or flaps of 

 the skin, which point towards the tip of the limb but do not 

 overlap one another. Their occurrence and gross appearance are 



