254 Distribution of Moths of the Sub-family Bistonince. 



from analogy. If we find such fragile plants as Podophyllum, 

 Stylophorum and Boltonia with precisely the same modern 

 habitats as Magnolia, Liriodendron and the rest, we can only 

 conclude that their histories coincide, i.e. that they once had 

 an enormous range in the huge Miocene Northern Continent. 

 Extending the argument from plants to other forms is again 

 perfectly natural, and the same conclusions must be drawn. 

 If the Bottle-nosed Sturgeons (Scaphirhynchi) and the Paddle- 

 fishes (Polyodontidce), and such Amphibians as the Amphiumidce 

 have likewise the same abodes nowadays, they too have 

 occupied, in earlier ages, the same far-flung extent of territory. 

 Finally, when we perceive insects like Amphidasys cognataria 

 with a distribution exactly similar to all of these many beings, 

 then it also has had the same vicissitudes ; it has once ranged 

 over the whole habitable Northern Continent. Amphidasys 

 cognataria then once increased and multiplied from the Rocky 

 Mountains eastward to the Miocene limits of Eastern Asia 

 and in areas, as the occurrence of fossils of Juglans and other 

 plants cited above there proves, far to the north. As a matter 

 of fact, the genus probably originated in North Eastern Pliocene 

 Asia, i.e. an Asia reaching far to the north of its present limits. 



Let us now consider what caused the breakdown of this 

 once continuous distribution. 



In earlier Pliocene times changes, tremendous in them- 

 selves, but when considered in respect to the northern land 

 masses as a whole not fundamentally altering the positions 

 of the great continents, occurred. Subsidences in the Northern 

 Arctic Regions took place ; North and South America became 

 united ; the Behring Straits were formed and so on. All of 

 these changes working together, possibly aided by external 

 factors effecting climate, brought about a marked alteration 

 for the worse in the climatic conditions of the Northen Hemi- 

 sphere, involving a general movement of all forms of life 

 toward the south. Forms pressing southward into America 

 and Eastern Asia, aided by the directions of the coast ranges, 

 had an easy passage, in one case taking refuge in lands around 

 the Gulf of Mexico and, when periods of subsidences set in, 

 in the Alleghany Mountains and, in the other, following 

 exactly the same direction and passing down the coastal 

 ranges, in South Eastern Asia. And we must not forget 

 that these migrating forms were in all areas almost identical. 



In Europe the same attempts were made ; here, un- 

 fortunately, the main mountain systems stretch from east 

 to west. Consequently, the path of the fleeing forms was 

 barred and many of the more tender temperate forms, including 

 Sassafras, Liriodendron, Magnolia and Onoclea, and hosts of 

 others were crushed out of existence before access to the 

 warmer regions of Southern Europe and Northern Africa 



Natural. st, 



