630 ^ PROF. J. COSSAE EWART ON THli 



months' Emu bred in the Gardens of the Zoological Society of 

 London) pi-ov^e conclusively that in the Emu the aftershaft in 

 origin and structure agrees with the shaft, while the feathers 

 represented in PI. VII. figs. 24 & 25 (from a much younger Emu 

 in the Museum of the Philosophical and Literary Institute, Leeds) 

 as clearly indicate that as the aftershaft is developed before the 

 calamus it cannot be an outgrowth from the calamus. The first 

 three generations of the feathers of an Emu are diagram matically 

 represented in text-fig. IL 



Before dealing with the aftershaft in the Carinatse, attention 

 may be directed to the remai'kable Emu feather of the second 

 generation represented in PI. VIII. fig. 28. In this growing feather 

 the aftershaft, instead of resembling the shaft, simply consists of 

 two barbs bearing barbules. An Emu feather with an aftershaft 

 represented by two simple barbs is interesting, because in ti'ue 

 feathers near the oil-gland of ducks two long barbs sometimes 

 occupy the position of an aftershaft. That the two long barbs in 

 this Emu feather represent a phase in the degeneration of the 

 aftershaft is suggested by PI. YIII. fig. 29, a developing true 

 feather with the protoptile intact from the rump of an eighteen 

 days' Mallard duckling. Connected with the protojDtile calamus 

 are two bundles of barbs — a large bundle with a distinct rhachis 

 which is obviously a developing shaft and a smaller bundle repre- 

 senting an aftershaft. The smaller or aftershaft bundle is con- 

 nected to the inner aspect of the protoptile calamus, as in the 

 Emu feather, by two long barbs. In course of time the large 

 bundle in PI. YIII. fig. 29 would have developed into a shaft like 

 the one represented in PI. I. fig. 1, and the small bundle into 

 an aftershaft with a short rhachis. Possibly long barbs which 

 represent an aftei'shaft will be met with in the feathei-s of other 

 Ratitas. 



The two long barbs in the Emu feather in PI. VIII. fig. 28 

 support the view that the coat of the adult Emu consists of true 

 feathers and not, as Py craft suggested, of mesoptiles. 



3. The Development of the Aftershaft of the True Feathers of 

 Fengmns. — In the Ringed Penguin the protoptiles though um- 

 belhform may be said to consist of two sets of barbs — an outer 

 representing a shaft and an inner occupying the position of an 

 aftershaft. Though in ducks and geese there is a well-developed 

 protoptile calamus containing " cones," in penguins as in the 

 Emu a true pi'otoptile calamus is never developed. Soon after 

 the protoptile escapes from its sheath the part of the epidermic 

 tube ]-epresenting a calamus splits into slender cords, which 

 connect the barbs of the protoptile with barbs of the developing 

 mesoptile. The mesoptile consists of a shaft made up of seven or 

 more simple barbs which end in the tip of the true feather, and 

 of a complex aftershaft connected with the aftershaft of the true 

 feather. In text-figs. 3 & 4 the mesoptile aftershaft is con- 

 nected to the aftershaft of the true feather by a narrow band 

 formed by the fusion of the distal portions of the barbs of the 



