618 , PROF. J. COSSAR EWART ON TUE 



are especially interesting, because they indicate how the suppres- 

 sion of the mesoptiles was gradimlly accomplished. In the case 

 of the disappearing protoptiles of the King Penguin (PI. 1. 

 fig. 4) the size is gradually reduced until they are smaller than 

 the minute bunch of barbs which precede the filoplumes of 

 ducklings. In the case of the vanishing mesoptiles two sets- 

 of factors are evidently at work ; one set arrests the development 

 of the mesoptile barbs, another set accelerates the development of 

 the barbs of the true feather, with the result that in coui'se 

 of time the tip of the true feather is found projecting into the' 

 base of the protoptile calamus. 



Though in most cases the mesoptiles are gradually reduced in 

 size, in some cases the length is maintained and either a few 

 barbs with barbules are developed, or the simple epidermic tube 

 splits into two or more bands, which for a time connect the 

 protoptile to the tip of the true feather. 



It may be mentioned that though all the wing-quill protoptiles 

 and mesoptiles may be present in the Mallard duckling at the 

 end of the sixth week (PI. III. fig. 12), some of the mesoptiles 

 are usually shed before the end of the seventh week, and all are 

 usually lost before the middle of the eighth week. But though 

 the wing-quills lose all their nestling feathers during the eighth 

 week, some of the feathers of the humeral track may retain 

 protoptiles and mesoptiles to the end of the eleventh week. The 

 existence of the wing-quill mesoptiles in the Mallard proves 

 conclusively that the nestling coat worn by newly-hatched Ducks 

 and Geese corresponds, not as Pycraft suggested to the second 

 generation of prepennse in Penguins, but to the first or protoptile 

 generation. 



(3) The Tail-Quill Protoptiles. ' 



The tail varies greatly in young aquatic birds. In Penguins 

 the tail protoptiles have almost disappeared and the mesoptiles 

 are only represented by a few simple barbs (PI. I. fig. 4). In the 

 Malla,rd the mesoptiles of sixteen of the eighteen tail-quills have 

 completely disappeared, but the protoptiles of all the eighteen 

 quills are larger and more complex than in the plumose (meta- 

 ptile) feather represented in PI. I. fig. 1. In Penguins steps are 

 soon taken to develop the tail-quills with a view to their forming 

 with the hind limbs a tripod useful in maintaining the erect 

 attitude. In the Mallard the protoptiles form a " nestling tail " 

 which plays an important part dui-ing the earlier portion of the 

 period tha.t Mallard ducklings behave like diving ducks*. 



In a ten days' duck embryo the tail-quill papillae t are easily 



* The adult Mallard, Mr. G. J. Millais informs me, " hardly ever dives except 

 when in play during the love chase, or to escape when wounded." 



f There are twenty tail-quill papillae, bnt only eighteen of them develop into 

 feathers large enough to rank as tail-quills. A paper " On the development of the 

 Feathers of the Duck during the Incubation Period " was recently communicated 

 to the Royal Society of Edinburgh by Augusta Lamont, B.Sc. 



