THE ENTOMOLOGIST. HI 



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 wdiich 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 autuum, as well as a spring, migration, 

 otherwise how are the insects jM'ovided 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 larva) 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. I am no believer at ])resent in the sportive theory ; 



* I am unable to see how rain in June would influence the growth of 

 vegetation in April, especially where so much raiu fulls annually as in 

 Nicaragua. — JI. H. 



