Page:Popular Science Monthly Volume 27.djvu/395

Rh questions and to matters apparently foreign to the immediate inquiry, that here the subject of the range of North American moths leads us into myth and poetry. For, in finding out that we have species of moths which are found in other continents, the question arises at once, How did they get here? They could not fly over from Europe, nor could they now cross Behring Strait, with the Arctic climate there existing. Imaginative persons have supposed a submerged Atlantic Continent, which bridged the chasm in a remote geological period. The myth of the Atlantis has been recently furbished up under the facts supplied by the deep-sea soundings of the English steamer Challenger, and the discovery of a plateau at the bottom of the ocean, between North America and Europe. But, if it ever existed, it probably did so at a time before the ancestors of our present moths came into being.

For a moment, let us leave this matter and look at the question of the affinities of our moths. I have shown, in the "American Journal of Science and Arts," the detailed characters of one family of our moths, the Sphingidæ, and what is true of them is true generally. Our moths, in regard to their structural relationship with the moths of the world, fall into three main categories: 1. Those which are peculiar to North America. 2. Those which have their nearest allies in South or tropical America. 3. Those which have their nearest allies in Europe or Northern Asia.

With these last we have here to deal, and to account for their presence with us. This class falls into two main groups—those which are absolutely the same, and those which differ more or less, but clearly reveal their common ancestry. But there exists in these respects every gradation. Some differ so little that there is much dispute as to whether they constitute different "species," and some, again, only differ perceptibly in certain stages. Others differ a little throughout in all stages, and form what are called "representative species." So, far off in Arizona, I have found a species (Copimamestra occidenta) which "represents" a common European species (Copimamestra brassicæ). What is this little moth, with its big name, doing in Arizona, and how did it get there? With regard to those kinds which are absolutely identical in America and Europe, some have evidently come over through commerce in historic times. We have found out almost the particular voyage which brought the "white-cabbage butterfly" from England to Quebec, whence the insect has spread over the New England and Middle States, to the great injury of our market-gardeners and cabbage-growers. But of some the distribution is such that this can not be the explanation of their presence here. Of others it may be doubtful. I am inclined to believe that another cabbage-insect, the moth called Pluria ni, has been brought over in this manner. But how about our Arizonian Copimamestra?

We shall have to leave entomology and go into geology to answer