MIGRATION AND DISPERSAL OF INSECTS} LEPIDOPTERA. 1838 
where it becomes exceedingly abundant in the autumn months. This 
irregularity in abundance is equally marked in both species, 1868, 1871, 
1892, and 1899 were among the abundant years for 4. archippus. Moffat 
says that near London, in Ontario, he has seen ‘ specimens arrive in 
the spring in a sorely faded condition, indicating age and exposure to 
the weather, followed by others that were comparatively fresh as if, 
they were younger and less travel-stained than the first. Then, again, 
the first arrivals are sometimes in fairly good condition, as if they had 
not been lone upon the wing ; whilst other specimens have been seen 
haunting a particular locality for weeks, and, as far as could be judged 
by their eradually fading colours, they were the same individuals.” 
He has also “ seen them flying plentifully for six or eight days and 
then begin to pair, indicating ‘that these particular individuals had not 
laid egos before reaching that locality ;” further, he has ‘‘ seen fresh- 
looking specimens flying at the time the new brood was emerging from 
the chrysalis, and so fresh as to give rise to a difference of opinion as 
to whether they were previous arrivals or bred on the spot.” Lastly, 
he had ‘“ seen quite small caterpillars on the milkweeds when others had 
passed into the mature state,” all of which has conyinced him that 
there is ‘‘more than one wave of migration northward during the 
breeding season.” All these irregularities of habit will be certain to 
strike one who has studied the subject, as being readily paralleled 
during a series of years by the immigrants of Colias edusa and 
Pyrancei is cardui, and their progeny in our own country. 
The species belongs essentially to the tropical and subtropical 
regions of the American continent. It is found all over the West 
Indies, as well as on the mainland, and extends south as far as 
Patagonia. During the winter no specimens are seen above 30° N. 
lat., in North America, and, at this latitude, but rarely; the only 
individuals that appear to get through the winter seem to be those 
that are well within the subtropical and tropical areas. The species 
is most probably continuously-brooded in the most favourable districts 
of its permanent winter home, and Edwards says that there are three 
or more broods in a season in Virginia; whilst in the more northerly 
part of its summer range—Hudson Bay district, and the basin of the 
Athabasca—one, and occasionally an attempt at a second, brood 
appears to be its maximum. Moffat states that it is quite clear that 
it cannot survive the winter in any stage of its existence in Ontario, 
or northward of it, and that each recurring winter sweeps the country 
clear of this particular species, and it has to be restocked every spring 
by immigrants from the south. Riley suspected that fertile females 
started northward in early spring, W hen the Asclepias was ready to re- 
ceive their ova, and travelled some distance before they had finished 
ovipositine, when these would naturally perish; then he supposed 
their progeny continued to advance and carry on the work of producing 
ova to stock the milkweeds as they came north, so that there might 
be several broods required in a season to reach the northern limits of 
its food-plant. Scudder claims, on the other hand, that it is a long- 
lived insect, that a female starting northwards may travel for w eeks, 
depositing her eggs as she goes, a few at a time, until she reaches the 
northern limit of the growth of the food- plant, and further asserts that 
the insect leaves its winter quarters later in the season than other 
butterflies, that it is ‘“‘simele-brooded,” that it ‘continues upon the 
