THE PTERYLOGRAPHY OF THE MEGAPODII. 487 



adult 10. There are no claws in the wing of the nestling Megapode, but they 

 appear for a while in the embryo. 



The manus and fore-arm of the ? 6 — 7 day embryo ai-e sub-equal in length, in 

 the nestling the manus is considerably shorter than the fore-arm. This diftereuce or 

 change in relative length of the fore-arm and hand has been already commented 

 upon in the Common Fowl and in Opisthocomus, in the paper just referred to (10). 



IV. The Pterylosis of the Embryo. 



In so far as the general form and proportions of the tracts are concerned, the 

 embryo, as already remarked, tloes not differ from the adult. Furthermore, it is 

 difficult, given embryos of the same relative stage of development, to distinguish 

 between those of the Common Fowl and those of the Megapode. In the stage 

 figured, the two forms may be certainly distinguished by the fiict that, in the Fowl 

 the wing is eutaxial and there is a rudimentary " comb," and in the Megapode the 

 wing is diastataxial and there is no rudiment of a comb. 



Concerning the diastataxial wing of this embryo (Fig. 4) I would remark only, 

 that it does not differ materially in the form and distribution of the shifting papillee, 

 from the normal diastataxial wing, as recentl}' described by me (12). There are no 

 claws on the wing of this embryo. 



The wing of a much earlier embryo than this exhibits one or two features of 

 great interest, and, I think, importance. 



In the first place, it appears to have already become diastataxial : the develop- 

 ment of the feather papillae is still very faint)}' traceable so that this point is 

 difiicult to make, nevertheless there is but little doubt that it is so. Furthermore, 

 the post-axial border of the distal end of the fore-arm has a swollen appearance, as 

 if the superficial growth had been faster than the deeper parts, so as to cause a 

 tendency which would ultimately end in producing a fold. It suggests that the rate 

 of gi-owth of the skin, and muscular tissue below, had outstripped that of the skeleton 

 withio. This has crowded the anterior cubital remiges together, and forced the 

 associated major coverts out of position, finally resulting in diastataxy. This swollen 

 stage is a noticeable feature in many diastataxial wings. I do not, however, in the 

 above facts see any reason to alter my recent explanation (12) as to the manner in 

 which diastataxy is brought about. I should regard them rather as secondary phenomena 

 probably not connected with the origin of diastataxy at all. 



The length of the hand in this stage is less than that of the fore-arm. 



This collection contains several embryos much younger than the last, and two of 

 stages much older than that here figured (Fig. 1). With the very early stages we 

 cannot deal in the present paper ; the later stages are useful — in the present connection — 

 only in so far as they afi'ord material for studying the nature and development of 

 the nestling plumage, and will be dealt with under this head. 



65—2 



