cclxxiv 



for such hibernation. Under the most favorable conditions a large ma- 

 jority perish. A portion of the females survive the winter. Such hiber- 

 nated individuals, upon awaking from their winter torpor, make at once 

 for the prairies, where the milk-weeds most abound. Faded, and often 

 tattered, they may be seen flying swiftly over such prairies, for the wings 

 of the species are strong and large. I have no doubt but that they travel 

 thus for many hundreds of miles, keeping principally to the north, and, 

 ere they perish, supplying the milk-weeds here and there with eggs. A 

 fresh brood is produced in less than a month, and these extend still farther 

 north, until we find the species late in the growing season as far up as the 

 Saskatchewan country, where it can scarcely successfully hibernate, and 

 from whence the butterflies instinctively migrate southward. We can thus 

 understand how there are two, three or more broods in southerly regions, 

 but only one toward British America. 



The exceptional flights noticed in the spring, and which, so far as re- 

 corded, take place quite early and in the same southerly direction, find a 

 similar explanation. They may be looked upon as continuations of the 

 autumn flights. Hibernating in the temperate belt, the butterflies are 

 awakened and aroused, upon the advent of spring, to find the milk- 

 weeds not yet started; and they instinctively pass to more southerly 

 regions, where the spring is more advanced. In short, these migrations 

 find their readiest explanation in the instinct of the species to lengthen the 

 breeding season and to extend its range,,and the prevailing winds at the 

 particular seasons are of a character to assist it. There is a southward 

 migration late in the growing season in congregated masses, and a north- 

 ward dispersion early in the season through isolated individuals — this dis- 

 persion keeping pace with the advance of spring toward the north. It is 

 a notable fact that the two butterflies which most display this migratory 

 instinct, viz., the species in question and the Painted Lady {^Cynthia car- 

 dut), have the widest range of known species. This last is cosmopolitan, 

 occurrring in all four quarters of the globe; while our Archippus, origin- 

 ally confined to America, though ranging from Canada to Bolivia, appears 

 to be following the milk-weeds, wherever these are, through chance or 

 purpose introduced. It has lately spread over some of the islands of the 

 Pacific to Queensland and New Guinea, and over the Azores to Europe — 

 such spread necessarily indicating great power of long-sustained flight, 

 since the milk-weeds are not plants of commercial value, and it is highly 

 improbable that the species has been carried in any of the preparatory 

 states on ships. 



It was suggested by the President that the Missouri Weather 

 Service might render itself useful in noting the migration of birds, 

 animals, insects, etc. 



Dr. G. Engelmann presented some engravings from an English 

 journal of a microscopic fossil fungus of the carboniferous forma- 

 tion allied to Peronospora infestans. 



