NOTES AND QUERIES. 389 



astonishment. The Locust, with its strong body and powerful wings, 

 cannot make head against the wind, but drifts with it ; yet that a butterfly 

 with a body so slight as scarcely to gain a fulcrum for the wings to 

 bear on, and with wings offering so broad a surface to the breeze that 

 one would expect to see it drift like a snowflake, should possess the 

 faculty of propulsion against a strong wind, gives us a clue to an 

 aerostatic principle with which we are not yet acquainted. It is to be 

 noticed that the action of the wings of these butterflies is not horizontal, 

 like the Admiral or the Tortoiseshell, nor is their flight even and con- 

 tinuous, but they are propelled in jerks, with the wings vertically closed and 

 opened alternately, so as to offer the sharpest edge to the resistance of the 

 wind. Thus the butterfly does not appear to propel itself, but to be driven 

 forward by the action of the wind eddying round against the under surface 

 of the wing presented to it; but how this is done it is not easy to 

 demonstrate. As there is no land south of Ceylon, it seems evident that 

 these butterflies deposit their eggs in the southern forests of this island, 

 previous to their starting on their migration ; otherwise the annual flights 

 could not be kept up. I notice, however, that Mr. Mann gives the months 

 of March and April as the season of migration witnessed by him ; but 

 while he gives the direction of their flight from N.E. to S.W., he does not 

 state the direction of the wind. The S.W. monsoon usually commences 

 in April, while the N.E. monsoon commences in October. I assume that 

 these are the same flights returning after a circuit of the island, and flying 

 against the southerly wind in the same manner as those seen by me in 

 November were flying against the north wind. I cannot identify Navan- 

 ghena, the place from whence Mr. Mann writes, and therefore do not speak 

 confidently. — E. L. Mitford (Pikdan House, Morpeth). 



Insect Migration, — The Clouded Yellow Butterfly (Colias edusa) is 

 one of the most interesting of British species, from its habit of appearing 

 in the more northern parts of Britain at irregular intervals — a peculiarity 

 which it shares in common with various other Lepidoptera. No satis- 

 factory reason for this erratic behaviour has yet been advanced, nor know- 

 ledge gained of how or in what stage of its existence the insect passes the 

 time between each appearance. In Scotland the first recorded capture of 

 C. edusa was made in Arran in 1848, by Mr., afterwards Professor Sir, 

 Wyville Thomson. Four years later one was captured near Largs, in 

 Ayrshire, on Sept. 12th, by the late Mr. Birchall. The next, or third, 

 Scottish specimen was secured at Kirkraahoe on Aug. 17th, 1857, by 

 Mr. W. G. Gibson; and in the same year a few more were taken about 

 Glencaple and neighbourhood. In 1859 some were seen near Newbie, and 

 in 1862 Mr. Lennon and other local collectors took it in large numbers in 

 this district. From 1862 till 1877 no one appears to have seen this 

 butterfly on this side of the Border, but in the latter year it suddenly burst 



