58 Trinnadions. 



4 lines, and the Aatiimn ones 2in. 1 line, thus showing a 

 difference of 3 lines or ]- inch. These measurements are 

 from my own specimens, and might be somewhat modified if 

 a moi-e extensive series was examined. 



Let us now briefly consider the various theories that 

 have been put forth to account for the appearance of Colias 

 Edusa after long years of absence. The first one is the 

 famous " Blown over theory " of the late Edward Newman, 

 which was that females were blown over by the wind from 

 France, and that these females deposited the eggs which pro- 

 duced the next year's flight of Butterflies, thus establishing a 

 colony that died out in a few years, again to be renewed in a 

 similar manner. However applicable this theory may be to 

 the extreme south of England, it will not account for the 

 appearance of the insect in more northern localities. Another 

 theory is, that eggs or pupae lie dormant until forced into 

 active life by influences of which we are yet ignorant. It 

 may be mentioned here that apparently the weather has had 

 no influence, for while in Scotland the season has been almost 

 unexampled for cold and wet, the pasture fields in the ex- 

 treme south of England have been quite scorched up with 

 drought, still Edusa has been everywhere abundant. 



On the Continent also, Edusa has been seen in much 

 scantier numbers than usual, thus showing that the cause 

 which has led to this abundance in our own country was in 

 operation in Britain only. The " Clover Seed theory" is one 

 which I think is entitled to more consideration than it has 

 hitherto received. To understand this one it may be as well 

 to explain that as the larvge of Edusa feed on various clovers 

 the oggs are deposited on these plants, and that when the 

 clover seed is harvested — which happens in August — the 

 eggs become detached and mix with the seed, and are thus 

 conveyed to this country if we require it, and ultimately 

 sown in our fields. My reasons for viewing this theory 

 (until another one is propounded) with favour are as fol- 

 lows : — During the Spring of 1876 clover seed of home 

 growth was not to be had, owing to a failure of the 



