PHYLOGENETIC 55 



the Indian Ocean. The " Sheath-bill " or " Kelp-pigeon " bears, 

 as its name implies, a by-no-means Plover-like aspect, but rather 

 a likeness to the Pigeons, which birds it further resembles in 

 its flight and methods of courtship. Snow-white in plumage, 

 it is remarkable in many ways, and especially on account of 

 the peculiar tubular sheath which covers the base of the beak, 

 giving the bird, in this particular, a semblance to the Petrels. 

 Natives of the extreme south of South America, the P'alklands, 

 Crozets and Kerguelen, this Plover is essentially a bird of 

 the seashore ; it is frequently indeed found far out at sea, 

 where it appears to be as much at ease in the water as more 

 aquatic types, such as the Gulls for example. Rut this bird is 

 further referred to elsewhere (p. 446). 



These aberrant types are of extreme interest, representing, 

 as it were. Nature's experiments at Plover-making. They are 

 at any rate ofTshoots which started on their several roads to 

 specialisation before the more typical Plovers began their evo- 

 lution. And this also is true of the Gulls and Auks. By the 

 older systematists, and some modern Ornithologists who judge 

 solely by appearances, regarded as allies of the Petrels, the 

 Gulls are nevertheless to be regarded as archaic but highly 

 specialised Plovers, the Skuas representing the earlier and the 

 Terns the latest phases of evolution. 



Just as the Gulls were, and still are by some, regarded as 

 allies of the Petrels, so the Auk tribe were, and are, regarded 

 as related to the Divers (Colymbi). Yet they have not the 

 remotest relation to these birds, but are on the contrary in- 

 tensely modified Plovers adapted for an aquatic mode of life 



(p. 450). 



By most authorities, and we think rightly, the Pigeons and 

 the Sand-grouse are included in this assemblage of Plover-like 

 birds. It is possible, however, that the older workers in this 

 case were right who saw in these birds Gallinaceous characters. 

 At any rate Dr. Mitchell holds that in so far as the evidence 

 of the convolutions of the intestines is concerned the Pigeons 

 and Sand-grouse, and that paradox the Hoatzin (Opisthoco- 

 mus) of South America, are all derived from a common stem, 

 running parallel with branches which gave rise to the Gallinaceous 

 birds, Tinamous and Turnices (p. 75). We cannot, however, 

 agree that other anatomical facts lend support to this view. 



