26 W. P. PYCRAFT. 



convolutions of the Colymbi, Sphenisci, Steganopodes, Ciconise, 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 

 alonff 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 

 Palamedese, 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 

 Phsethon is holothecal ; and what is somewhat remarkable, so also is Plotus, while in the 

 nearly allied Phalacrocoracidae the sheath is still compound. 



That the deep lateral grooves along the rhamphotheca of the penguins, extending 

 almost to the tornium, 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 Charadrise, as well as of many Ciconise and Rallidse. 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 Eudyptula are less specialised than Catarrliactes 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 



