BY R. J. TILLYAUD. 403 



which AuntrodesrhiKi p<irvisti(jiiia, var. multipunctafa, is the 

 commonest) appear laft^ in the season, and their larvae are not 

 more than half-grown by the time that of (J. montana is full- 

 fed. Hence we have a striking instance of two closely allied 

 species adapting themselves to circumstances, in two opposite 

 ways, which achieve the same end; viz., along the coast, 

 where the commonest .4 eschmd emerges very early in the 

 season (Aesr/itia hrevhti/hi is on the wing from October to 

 December) we have (\ pi/duura emerging late; whereas on 

 the mountains, where all* the Aeschniche emerge late, we 

 have C. montana emerging early. This may seem remark- 

 able, in view of the fact that the mountain-climate is so 

 much colder, and the season so much later. But if we con- 

 sider the fact that the mountsiin- AeschnidcF are on the wing 

 right to the end of February, by which time the season for 

 dragonflies is practically over, and the weather getting cold 

 again, we shall see that the early emergence of C. inoiif/ina 

 was absolutely necessary to preserve the species. 



I offer, for what it is worth, an interesting theory to 

 account for this discrepancy. It is well known that oiir 

 commonest species of the CordnUino',, Hetnicordtdia taii, is 

 distinctly double-brooded. They emerge in great numbers 

 from September to November, and then again in February 

 and March, or even April. The second brood, however, is 

 not so constant as the first in point of abundance, being 

 usually less numerous, though occasionally, for some unex- 

 plained cause, exceedingly abundant. Now, in the habits of 

 its early stages, Cordideyhya resembles Tlemirordidia very 

 closely. Assuming then that there was a time when the 

 former was much more common than it is now, and that it 

 originally occupied, in the Australian Odonnte fauna, some- 

 what the same position that TI emicordidia does at present, 



* I ought to except JR. Itrevistyla, which occurs jj«»v apdringly on the 

 mountains, and is on tlie wing in December; but it is not at all common 

 there. 

 35 



