152 B. p. UVAROV. 



These latter consisted, as Dr. La Baume stated after a study of the specimens, of 

 nii°^ratorioides, while the March swarms, again according to his determination, were 

 composed of danica, which leads him to the conclusion that they could not possibly be 

 the direct progeny of the December swarms. I believe, however, that Dr. Sander 

 (who simply did not distinguish migratorioides from danica) was right, and that the 

 December swarms of migratorioides actuallj' produced the March swarms of danica. 



All these facts, of course, do not furnish us with absolute proof of the trans- 

 formation of migratorioides into danica ; but since such a transformation is firmly 

 established for migratoria and danica, I feel justified in assuming it to be true in this 

 case also. 



Geographical Distribution. 



Of the three forms here dealt with, danica has the most extensive range ; in 

 fact, it is found throughout the whole of the Eastern hemisphere, except the coldest 

 regions beyond 60"^ northern and southern latitude, very high mountains* and vast 

 waterless deserts. As for the Western hemisphere, though many books state that 

 danica occurs in America, I know of no reliable evidence to this effect, and am fully 

 convinced that all the older records are due to mistakes, either in labelling the 

 specimens or in their identification.** Thus, F. Walker described Pachytylns hrasi- 

 liensis. which is conspecific with danica, from a specimen in an unlabelled collection 

 which included insects not from Brazil only, but from other parts of the world also, 

 and the mistake in locality in this case is beyond doubt. 



A form with such an enormous area of distribution may be expected to present 

 some geographical variations, and in fact, apart from the individual variability 

 which, as I have already stated, is very great in danica, some more constant varia- 

 tions, probably connected with geographical conditions, are also observed. Thus 

 Australian and New Zealand specimens are rather small on the average, with a 

 comparatively short pronotum and the wings slightly infumate ; they ha^'e been 

 described by Saussure as a distinct species, Pachytylns anstralis, Sauss. As, however, 

 no one has yet studied extensive series of individuals of Australian origin, the 

 constancy of these characters is not proved ; on the other hand, specimens of the 

 same kind occur incidentally in other localities as well, and their distinctions from 

 the typical danica do not exceed the average extent of observed individual variability. 

 Again, as I have already pointed out (p. 139), there is a slight difference between 

 the individuals of danica from the Palaearctic region and those of tropical origin, 

 which also may depend on geographical conditions ; but in this case likewise more 

 extensive investigations are wanted. 



The area of distribution of migratorioides, though not so extensive as that of 

 danica, still occupies the greater part of the latter, in fact the whole of it except 

 the Palaearctic region. 



The latter region is the home of migratoria, which is however common in its 

 south-eastern parts only (especially in the basin' of the Black, Caspian and Aral Seas 

 and that of Lake Balkhash), where its permanent breeding grounds are, while its 

 emigrating swarms penetrate much farther north and westwards, sometimes as far as 

 Finland and England. On the other hand, single individuals, which agree in all their 

 morphological characters with migratoria, occur far beyond the Palaearctic region 

 as well. Thus, Brunner v. Wattenwyl recordedf migratoria from the Malay 

 Archipelago (Batjan and Borneo). I have myself seen a quite typical specimen of 



* I have recorded (Revue Russe d'Entom., xiv, 1914, p. 232) this form from the Pamir upland 

 as high up as 11,000 ft. above sea-level ; there is in the British Museum a couple of specimens 

 taken at Giangtse, Tibet, at an altitude of 13,000 ft. 



** Dr. J. Rehn, of Philadelphia, informed me recently that he is of the same opinion. 



t Abh. Senkenberg. Naturf. Ges., xxiv, pp. 194, 196. 



