ON A DARK FORM OF ISCHNURA ELEGANS. 253 



taken on July 17th, 1904, however, exhibited a distinct trace of 

 blue on the ventral surface of segment eight. 



Apart from any other points of difference already indicated, 

 our specimens are readily distinguishable from individuals of the 

 typical form, whether in the mature or the immature state, by 

 the dark-brown or blackish colour of the eighth segment. They 

 are separable from the orange variety of the female (to which 

 Stephens gave the name rufescens) by the substitution in the 

 former of olive-green for the bright orange of the thorax charac- 

 teristic of that variety ; the first and second segments of the 

 abdomen, instead of being orange, as in var. rufescens, exhibit, 

 in our specimens, black or green-black markings of the usual 

 form upon a ground-colour of olive-green. 



We are convinced that most, if not all, of the insects under 

 consideration are fully matured ; but, as doubts have been sug- 

 gested as to their maturity, we may say that our conviction is 

 based upon the following considerations : — 



(1) We have taken no less than two of them in copulation or 

 connected per collum, and we have never known a dragonfly to 

 pair with the opposite sex until full maturity has been attained. 



(2) The immature coloration of such species as we are best 

 acquainted with is lighter, not darker, than the mature colora- 

 tion. Now, the colour of segment eight in the individuals before 

 us is much deeper in tone than the normal blue colour. The 

 colour which usually precedes blue in dragonflies is well seen in 

 immature males of Agrion puella and Enallafinia cyathigerum. 



(3) Only a few examples of the dark form are met with. If 

 that form represents a constant phase in the colour-development 

 of the female, it ought to occur very frequently, for the species 

 is quite a common one with us, and we keep it under close 

 observation. 



(4) In spite of the circumstance that, quite at the end of the 

 season, other collectors have obtained specimens of /. elegans 

 with the immature colouring, we are of opinion that some weight 

 should be attached to the facts that none of our examples have 

 been taken prior to July 3rd, and that one of them occurred so 

 late as September 4th ; indeed, the last-named (the dark female 

 of September 4th this year) was the sole representative of the 

 species we had come across since August 7th. 



(5) Most of our specimens present, when newly taken, a 

 distinctly dusty appearance, somewhat resembling the bloom 

 upon a black plum ; we have sometimes observed the same ap- 

 pearance in specimens of other species taken late in the season. 



(6) The wings retain no trace of the high gloss of immature 

 wings. 



We think it likely that this form may be a reversion to the 

 ancestral type. The coloration of the normal female approxi- 

 mates to that of the male much more closely than is usual 



