NESTLING FEATHERS OF THE MALLARD. 641 



Plate III. 



Pig. 9. Filaments from a 13 clays' Mallard embiyo ; tlie long filaments contain 

 developing protoptiles, the small ones preplumulse or prefiloplumse. 

 X2. 



10. Win^-quill protoptile artificially removed from a filament of a 26 days' 



Mallard embryo. 



11. Aftershaft of the protoptile of a duelling. 



12. Wing of a 38 days' Mallard duckling showing mesoptiles between the pro- 



toptiles and the developing primary and secondary wing-quills. Lying 

 between developing wing-quills (each still invested by a sheath) are wing- 

 coverts in which the mesoptile is vestigial. 



Plate IV. 



Pig. 13. Protoptile, mesoptile, and tip of wing-quill of a Chinese gosling. Though 

 the mesoptih^ seems to be umbelliform and to end in a calamus, it really 

 consists of a shaft and an aftershaft from wdiich slender threads proceed 

 to the tip of the true feather. 



14. In this figure the proximal portion of the mesoptile is represented. It con- 



sists of a narrow, perforated band representing the rhachis of the meso- 

 ptile shaft, of a broad perforated band representing the rhachis of the 

 aftershaft, and of numerous slender threads which connect these bands 

 with the shaft and the vestigial aftershaft of the true feather. 



15. Nestling tail of a 7 days' Mallard ducldiug. The protoptiles at each side 



of the middle line have beeh pushed from the skin by the developing 

 true tail-quills. 



16. The "nestling tail" at the middle of the fifth week. It now consists of 



growing true tail-quills as well as of protoptiles, usually with the ex'cep- 

 tion of the ninth from the middle line at each side the protoptiles are 

 directly continuous with the tail-quills — in other words, in the tail of the 

 Mallard duckling nearly all the mesoptiles have been completely 

 suppressed. 



Plate V. 



Fig. 17. Nestling feathers from the back of a 33 days' Mallard duckling. The large 

 protoptile has a distinct calamus containing "cones." To the left of 

 the calamus are : (1) a filoplume with a minute prefiloplume on its tip; 

 and (2) two plumula; each carrying a preplumula, to the right a plumula 

 with a preplumula on its tip. X 5. 



18. A plumula from a young Aylesbury duck showing a large shaft consisting 



of long, slender barbs springing from a relatively short rhachis and a 

 well-developed aftershaft with a short rhachis. 



19. The calamus of a naturally shed plumula with part of the sheath of the 



growing plumula attached. 



20. A developing filoplume with a prefiloplume at its tip from a 7 weeks' 



Aylesbury duckling. X 2'5. 



Plate VI. 



Fig. 21. Developing plumula from a 5 weeks' duckling. The aftershaft is developing 

 from apex to base in exactly the same way as the shaft. X 4. 



22. A protoptile from a young Emu showing an aftershaft with a short 



rhachis. 



23. Emu feathers of the first (protoptile) and second generation. The protoptile 



shaft is directly continuous with the shaft of the second feather, and the 

 protoptile aftershaft is continuous with the aftershaft of the second 

 feather. 



Plate VII. 



Pigs. 24 & 25. In 24 we have an early stage in the development of an Emu feather of 

 the second generation. In 25 the development of the second generation 

 feather has been nearly completed. In both cases the aftershaft is deve- 

 loped in the same way as the shaft — the tip of the aftershaft of the 

 second feather is continuous wnth the protoptile aftershaft and the tip of 

 the shaft is continuous with the protoptile shaft. 



