166 THE ZOOLOGIST. 
beyond latitude 70° N.; the remaining genera do not extend 
so far. 
Professor Heer records as a very interesting fact that in 
Grinnell Land two twigs of the spruce (Pinus abies, Linn.), still 
covered with leaves, were found. He had already received single 
detached leaves from Spitsbergen; with them there were seeds of 
this species, and, further, there was also found a scale of the cone, 
so that the species could be determined with-perfect certainty. 
We therefore see that our spruce was.living during the Miocene 
period in Grinnell Land as well as in Spitsbergen, and at that 
time doubtless extended as far as the Pole—at least, if any dry 
land then existed there. In Europe the tree did not then exist; 
hence, in all probability, it had its original home in the extreme 
north, and has thence extended southwards. Its extreme northern 
limit is now in Scandinavia, latitude 693° N.; and it is now 
spread over about twenty-five degrees of latitude, whilst during 
the Miocene period it was limited to the Arctic zone.* 
It appears to me that these conclusions of Professor Heer 
must be of very great importance to every zoologist who-makes 
the origin of species a study. If our common spruce, as he 
demonstrates, originated at the Pole itself in Miocene times, 
and has gradually extended southwards in consequence of the 
cooling of our glohe, it is surely not unreasonable to suppose 
that various species of plants and animals have accompanied the 
spruce in its movements southward until checked by the increase 
of temperature. Unless some such theory as this be admitted, 
it is difficult to account for the distribution of certain animals in 
the northern hemisphere. 
As an example, let us refer to certain species of birds which 
may be denominated Arctic species, such as the Ivory Gull and 
Ross's Gull. Mr. Howard Saunders has recently publishedt a 
valuable essay on the geographical distribution of the Gulls 
and Terns; and the conclusion he arrives at is that the bulk of 
the evidence adduced indicates the North Pacific as the centre 
of dispersal of the Laride. Mr. Saunders, however, expressly 
excludes the two isolated and specialized genera of Gulls, Pago- 
phila and Rhodostethia, from his generalizations, as they are not 
known in the North Pacific. Pagophila and Rhodostethia can only 
* Heer, ‘Quarterly Journal Geol. Soe.,’ February, 1878. 
+ ‘Journal Linnean Society,’ Zoology, vol. xiy, 
