DIVERTICULUM 153 
validity of which is not yet fully recognized. The Divers live 
chiefly on fish, and are of eminently marine habit, though invari- 
ably resorting for the purpose of breeding to freshwater-lakes, 
where they lay their two dark-brown eggs on the very brink; but 
they are not unfrequently found far from the sea, being either 
driven inland by stress of weather, or exhausted in their migra- 
tions. Like most birds of their build, they chiefly trust to swim- 
ming, whether submerged or on the surface, as a means of progress, 
but once on the wing their flight is strong and they can mount to 
a great height, whence on occasion they will rush downward with 
a velocity that must be seen to be appreciated, and this sudden 
descent is accompanied by a noise for which those who have wit- 
nessed it will agree in thinking that thundering is too weak an 
epithet. In winter their range is too extensive and varied to be 
here defined, though it is believed never to pass, and in few direc- 
tions to approach, the northern tropic; but the geographical dis- 
tribution of the several forms in summer requires mention. While 
C. septentrionalis inhabits the north temperate zone of both hemi- 
spheres, (. arcticus breeds in suitable places from the Hebrides to 
Scandinavia, and across the Russian empire, it would seem, to 
Japan, reappearing in the north-west of North America,! though 
its eastern limit on that continent cannot yet be laid down; but it 
is not found in Greenland, Iceland, Shetland, or Orkney. C. 
glacialis, on the contrary, breeds throughout the north-eastern part 
of Canada, in Greenland, and in Iceland. It has been said to do 
so in Scotland as well as in Norway, but the assertion seems to 
await positive proof, and it may be doubted whether, with the 
exception of Iceland, it is indigenous to the Old World,? since the 
form observed in North-eastern Asia is evidently that which has 
been called C. adamsi, and is also found in North-western America ; 
but it may be remarked that three examples of this form have 
been taken in England, and two in Norway (Proc. Zool. Soc. 
_ 1859, p. 206, Nyt Mag. for Naturvidenskaberne, 1877, p. 218, and 
Stevenson’s birds of Norfolk, iii. pp. 268, 269). 
DIVERTICULUM (a. cecum vitelli). After the yolk-sac has 
been withdrawn into the body-cavity its stalk remains in connection 
with the small intestine, and forms an appendix to it like a little 
cecum, which often persists throughout life in the NIpIFUGa, and 
1 Mr. Lawrence’s C. pacificus scems hardly to deserve specific recognition. 
2 In this connexion should be mentioned the remarkable occurrence in 
Europe of two birds of this species which had been previously wounded by a 
Weapon presumably of transatlantic origin. One had ‘‘an arrow headed with 
copper sticking through its neck,” and was shot on thie Irish coast, as recorded 
by Thompson (Nat. Hist. Ircland, iii. p. 201); the other, says Herr H. C. 
Miller (Vid. Medd. nat. Forening, 1862, p. 35), was found dead in Kalbaksfjord 
in the Froes, with an iron-tipped bone dart fast under its wing. 
