104 MR. C. N. BARKER ON 



half the year and under that of the S.W. Monsoon for the 

 other half. This probably produces a considerable inter- 

 mingling of Eastern and Western forms. This disposition 

 to rjnge from district to district, now in an easterly, now in 

 a westerly direction, not always as the wind blows, but 

 influenced by it as to the general trend, is probably always 

 existent. The migrations of great ho«ts is evidently of 

 rarer occurrence and may be governed by the same laws, 

 whatever they may be, that affect the movements of the 

 locusts. Under these conditions it is hardly to be wondered 

 at, that there is occasional instability among seasonally 

 dimorphic forms in certain districts of India and elsewhere 

 caused by the influx of new stock, interbreeding with that 

 which has been longer resident, and thus interfering with 

 the regular sequence of dimorphism. The areas affected by 

 these migrants are naturally of a limited extent, and, as in 

 the case of locusts, are of great consequence to one district, 

 whilst leaving those adjacent unaffected. Hence we have the 

 divergences in the testimony of observers in different parts 

 of the same country, which are often so conflicting in their 

 nature. For instance, we have the fact recorded by 

 de Niceville that the different forms of Catopsilia py ran the, 

 though corresponding to the seasons in some parts of their 

 range, are indej)endent of them in others. He goes on to say 

 that it is not seasonally dimorphic in Sumatra as it is in 

 India. In Ceylon, where four forms of this species are re- 

 corded by Moore, Manders says tliey ap[)ear all the year 

 round as sim[)le varieties. On the other hand, he says," True 

 C pyranthe is not common in Missouri in the rains ; the 

 dry season form C. gnoma, F., even less so. In the Dun 

 both forms are common in their respective seasons." Both 

 these places are in the district of Garhwal, N. India. Again 

 we have the exj)erience of Mr. Dudgeon in tlie Kangra 

 Valley, W. Flimalayas, who captured a large number of 

 Catopsilia crocale, Cr., and C. p onion a, /'., on the same 

 day (August 12th, 1900). They are stated to have formed 

 part of a migratory flight which lasted all day. The case of 

 Col. Yerbury's Aden and (Jol. Swinhoe's Karachi experiences 



