Canon Tristram on the Polar Oi'igin of Life. 215 



Pacific route, by Kamscliatka and Japan. All the East- 

 Asiatic species, some thirteen in number, with the doubtful 

 exception of T.javanicus, appear to be strongly migratory 

 in their habits ; all reverting to N.E. Asia for nidification, 

 and thus indicating the route by which their ancestors first 

 set forth. It is very possible that these species, as well as 

 many of those which adopted other routes, had become segre- 

 gated before their final departure from the Arctic continent. 

 Mr. Seebohm would explain this by the theory of successive 

 emigrations during successive glacial epochs, the species 

 being developed in different southerly regions during isola- 

 tion from kinsfolk, and then returning with the retrocession 

 of the ice. The species now having become perfectly distinct, 

 set forth again at the next glacial epoch, each of those species 

 being the generic progenitor from which many existing species 

 have evolved. Without denying the possibility of this hypo- 

 thesis, 1 think that one partial glacial epoch may explain 

 approximately the existing conditions of the Thrush family. 

 I have taken the Thrushes as one illustration, and I think 

 a similar method might be applied in the treatment 

 of all the principal families. I do not think that there is 

 any evidence of a South-Polar origin for any of our land- 

 birds, any more than for any of our Flora above the lowest 

 cryptogams. I have already, in my last paper, admitted the 

 probability of the southern origin of the Penguins — a conjec- 

 ture strengthened by the recent demonstration of the struc- 

 tural difference between the wing-feathers of this and any 

 other known family. Perhaps the Petrels might be added as 

 of probable southern origin ; by far the larger proportion of 

 species being inhabitants of the Southern Ocean, while the 

 curious habit of nesting in burrows near the tops of moun- 

 tains, away from their ordinary haunts, may have been 

 derived from the absence of any low-lying land in the Ant- 

 arctic continent. 



A southern origin has also been suggested for the 

 Swallows. I fail to see the force of the arguments in 

 support of the hypothesis. All Swallows, like all other 

 birds, breed at the northern limit of their range, — a fact. 



