324 BIONOMICS, ETC. [CH. 



to depress the wings. Many of the smaller forms are very quick 

 "off the mark," but the larger Trameini are very clumsy and easily 

 captured. The most difficult genus to capture, known to me, is 

 Aethriamanta, which is always a few feet up in the air (when one 

 strikes at it) above the position one believed it to occupy! 

 Cordulephya rests on rocks or tree-trunks with wings closed; 

 but it is very quick at the take-off, and not easy to catch. 



The question of protective colouring need not be gone into 

 here; the reader is referred to chapter xm, from which he can 

 draw his own conclusions. The bright red tip developed on the 

 abdomen of certain very small Libellulinae (Plate I, fig. 2) gives 

 these insects a vicious and wasp-like appearance, but is not a case 

 of true mimicry, since no true wasps occurring with them have 

 a similar coloration. 



Size (Plate I). 



No Dragonfly at present existing can compare with the immense 

 Meganeura monyi of the Upper Carboniferous, whose expanse of 

 wing was somewhere about twenty-seven inches. The Liassic and 

 Jurassic Dragonflies were not very markedly larger than those 

 of to-day, except perhaps in the average size of the Zygoptera. 

 This latter suborder has undergone, on the whole, a progressive 

 reduction in size and wing-venation, culminating in the smallest 

 known forms of to-day. On the other hand, the Pseudostigmatinae 

 have all the marks of a hypertrophied group, and may be rightly 

 considered to be now much larger than the more Platycnemine-like 

 ancestors from which they probably sprang. 



As size cannot be measured by any single character, I have 

 selected three points on which we may judge the size of a Dragonfly. 

 These are (i) length of abdomen, (ii) expanse of wings, and 

 (iii) robustness. 



(i) Length of abdomen. There is nothing to approach the 

 Pseudostigmatinae (PI. I, fig. 8) in this, but the abdomen in this 

 group is excessively slender. The longest abdomens in robust 

 species are found in Petalura and Tetracanthagyna 1 . The shortest 



1 Dr F. F. Laidlaw (in litt. ) has recently informed me of the discovery in Borneo 

 of a species of this genus exceeding in size any Dragonfly yet described. I have, 

 however, no details concerning this. 



