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to explain this phenomenon, I cannot say, it is true, that I have quite explained 

 the cause of it, but my researches have cleared the way for it more than any 

 hitherto, and have in this respect made our knowledge advance a good deal. 

 They not only prove sufficiently that the above-mentioned far-spread notion 

 about migration, either from want of food for the butterflies themselves, or 

 with the purpose to bring the eggs where there will be enough food for the 

 larvae, or perhaps for reasons of generation, is not seriously supported by facts, 

 but also that probably no real migrations take place at all. Probably all 

 butterflies of species which are capable of it, fly at certain times in a special 

 direction in consequence of some influences not yet known to us, a fact which, 

 though often happening in some seasons at least, only then draws the attention, 

 when such a species is at the same time very abundant, and for this reason 

 many such butterflies are continually seen, all flying in the same direction. 

 In Java I have several times seen individual butterflies of the above-mentioned 

 species fly in this peculiar and uncommon manner, which I know so well, and 

 I think I may connect herewith an observation, made by R. Trimen who maintains 

 that it is a general property of the Pieridae to fly straight on and with power, 

 often all in the same direction, every now and then sitting down on flowers, 

 but not visiting all the flowers of the same plant one after the other, as 

 other butterflies generally do. To put this down as a general rule does not 

 agree, however, with my researches, but, therefore, I do not think it improbable 

 that this notion is founded on observations made in cases when evidently 

 meteorological influence caused the butterflies to fly in this peculiar manner, 

 there being at the same time only so few insects, that Trimen did not recognize 

 the so-called migration. In the same manner we might perhaps also explain 

 the fact which in any other way is rather incomprehensible, that the Catopsilia 

 Chryseis Drury, already mentioned, is seen in Ceylon to migrate every year 

 in large numbers, whereas this never happens with the same species in Java, 

 although the same phenomenon is very common there also in respect to 

 Catopsilia Pomona F. For the first mentioned species is very common in 

 Ceylon, whereas in Java it is not exactly rare, but not at all numerous. 



Nor in Australia either does this species seem to appear in great flights, 

 but though it is a rather common species there, according to Rainbow, it 

 has not been proved that it is sometimes very numerous there. So in Australia 

 great flights of Pieris Java Sparrm L. may be seen, but this is never the 

 case in Java, where this butterfly is not at all rare. Probably these species 

 could not multiply strongly in every region. Not every year do the great 

 flights of C. Pomona F. show themselves in Java and according to my obser- 

 vations it is probably when it does happen, it is due to the circumstance that 



