266 STUDIES IN THE LIFE-HISTORIES OF AUSTRALIAN ODONATA, 



of Petalura smooth; while the joints of the latter are considerably 

 longer and narrower than those of the former. It should be 

 noticed that, in each, the fourth or middle joint is the shortest. 



Like Petalura, Tachopteryjc deposits its eggs in wet boggy 

 places where there is scarcely any water. The habits of the two 

 nymphs are probably exceedingly similar. 



The only other Pe<«Zitri/ie nymph known is that of Uropetala 

 carovei White, ^discovered in New Zealand, and figured by Hudson 

 ('' Neuroptera of New Zealand "). The figure is a " popular " 

 one, badly drawn, and nothing can be gathered either from it or 

 the description. 



If any lesson is to be drawn from the study of the early stages 

 of Petalura, it seems to me to be that it is in reality a nearer 

 approach to the jEschnine type than the Gomphine. If we could 

 go back far enough to find the common ancestor of the two, 

 would not its nymph show considerable similarity to that of 

 Petalura ? We might even trace the divergence of the two 

 groups from one simple circumstance, viz., the natural selection 

 of running water or stagnant marsh for the passing of the early 

 stages. Given the former, it is clear that the ovipositor of the 

 female would be brought more and more into use as a true 

 "borer" by means of which the eggs might be safely lodged in 

 stems in the quiet corners of a rushing stream; the body would 

 become more slender, the antennae more filiform; and the whole 

 insect more active, thus producing the clean-living ^Eschnid 

 type. On the other hand, if the female continued to deposit 

 her eggs in the mud, what more natural than that she should 

 gradually relinquish the use of the " borer " and just drop them 

 into the mud, like the Gomphince I And the egg itself, being 

 no longer inserted into a narrow cleft, but merely dropped, would 

 tend to assume the more spherical form now found in all those 

 families where the boring apparatus of the female has, gone out 

 of use. Later on, at a time perhaps when the huge swamps of 

 the Mesozoic age were drying up and giving place to definite 

 stream-beds, these early ancestors of the Gomphince would again 

 be compelled to take to the rivers, where they would naturally 



.^^ .: 



