THE ENTOMOLOGIST. 111 
similar migrations in South America, Ceylon, &c., but none 
seem to give any Satisfactory explanation of why these 
migrations should annually take place. Mr. Belt, 1 think, 
nearly hits on the probable solution when he says: “ I thought 
that some of the earlier flights in April might be caused by 
the vegetation of the Pacific side of the Continent being still 
parched up, whilst on the Atlantic slope the forests were 
green and moist; but in June* there had been abundant 
rains on the Pacific side, and vegetation was everywhere 
growing luxuriantly ; neither would their direction from the 
north-west bring them from the Pacific, but from the interior 
of Honduras and Guatemala: the difficulty is that there are 
no return swarms.” If this be correct—and I believe Mr. 
Darwin, Mr. Bates, Mr. Holdsworth, and a host of other 
eminent authorities, incline to this view—we can advance so 
far on the stage of enquiry as to set down for certain that the 
migration takes place after the eggs have been deposited on, 
or near, the food-plant, otherwise the species would become 
extinct in the north-west quarter, from which it started in two 
or three years at the most. Is anything known of the food- 
plant of either of the migratory species of butterflies? If so, 
does it occur in patches widely separated, or is it generally 
distributed along the whole route of migration? Cannot 
Mr. Bates or Mr. Holdsworth give us some information on 
this point? I fancy, although not observed by Mr. Belt, that 
there must be an autumn, as well as a spring, migration, 
otherwise how are the insects provided for the next spring 
flight, except the eggs be deposited before the insects leave 
the immediate neighbourhood where they were hatched? I 
take it, that if there is no hybernation of insects in tropical 
countries, there can be little necessity for this provision of 
Nature during an almost perpetual summer. It would cer- 
tainly be helping us in the enquiry if we knew (1) whether 
the migratory flights consist of both sexes, and (2) whether 
the larve are found feeding in the districts vacated by the 
imagos? This would probably give a clew to the cause of 
migration: it would tend to show whether sportive or of 
necessity. Iam no believer at present in the sportive theory ; 
* Tam unable to see how rain in June would influence the growth of 
vegetation in April, especially where so much rain falls annually as in 
Nicaragua,—H. R. 
