26 W. P. PYCRAFT. 
convolutions of the Colymbi, Sphenisci, Steganopodes, Ciconiz, Accipitres and Anseres 
were derived from a common metacentre ; but that those of Colymbi were more primitive 
, than those of the Steganopodes, Sphenisci or Tubinares. The Steganopodes, indeed, in 
this particular represented a new metacentre from which the penguins and petrels, in 
common with the storks and diurnal birds of prey, took their rise, each group evolving 
along a radius of its own. This agrees extremely well with the characters which I have 
brought forward, drawn from the plumage and skull in the present connection. His 
scheme also embraces all the forms included in Dr. Gadow’s Colymbo-pelargomorphine 
brigade. But we should possibly be nearer the truth in regarding the Steganopodes as 
representing the stock from which these several orders were derived, and not the 
Palamedee, as the evidence of the intestinal convolutions alone would seem to indicate. 
With regard to the question of the compound rhamphotheca in the penguins, there 
can be little doubt but that the primitive beak-sheath was composed of several separate 
pieces, and that in the Tubinares these have attained their highest phase of develop- 
ment, while in other groups there is a tendency for these plates to fuse: so much so, 
that in each group exhibiting this type of rhamphotheca some members will be found 
in which all traces of distinct plates have been lost. Thus among the Steganopodes 
Pheethon is holothecal ; and what is somewhat remarkable, so also is Plotus, while in the 
nearly allied Phalacrocoracide the sheath is still compound. 
That the deep lateral grooves along the rhamphotheca of the penguins, extending 
almost to the tomium, are relics of distinct lateral plates (labials) there can be no doubt ; 
but if this sheath is on this account to be regarded as compound, so also must that of 
the long-billed Charadriz, as well as of many Ciconiz and Rallide. But this sheath in 
the penguins differs further from that in the Tubinares, since it lacks all trace of the 
‘‘ rostrale,” so well developed in the Tubinares and Steganopodes. 
As a factor in classification, there can be no doubt the structure of the beak-sheath 
is valueless, that is to say, it is of no value in determining questions of affinity ; 
inasmuch, as Dr. Lonnberg (10) has recently shown, traces of these originally separate 
elements occur more or less distinctly throughout the whole class Aves. 
As a measure of specialisation this character is certainly useful. Thus Aptenodytes, 
Pygoscelis, and Hudyptula are less specialised than Catarrhactes or Spheniscus, although 
in the former of these two the plates are greatly thickened, simulating those in the 
rhamphotheca of the Tubinares. 
Perhaps the most interesting facts which this enquiry has brought out are those 
connected with the nature of the nestling plumage, and the light they throw on the 
probable character of the primitive plumage. But these points have been dealt with so 
fully (p. 10) that there is no need to deal further with the matter here. 
Though the method of moulting in the penguins differs from that in all other 
birds, it is not, as has been stated, comparable in any way to the sloughing of the skin 
in snakes (p. 13); while for the sloughing of the lateral rhamphothecal plates of the 
lower jaw, described by Dr. Wilson, we may find a parallel in the shedding of a part of 
