36 BRITISH INSECTS 



ing is effected by means of thread-like or leaf-like gills, 

 within which the tracheal tubes ramify. These are 

 not found on the thorax, as in the case of the stone- 

 fly nymph, but are arranged in pairs at the sides of 

 the abdominal segments. 



Albeit the young May-fly differs widely in appear- 

 ance from its adult form, its metamorphosis is incom- 

 plete, no quiescent or pupal stage being assumed. 

 When the nymph is full grown, it creeps out of the 

 water, its skin splits down the back, and the winged 

 insect appears. But the transformation is not yet 

 complete, for May-flies undergo their final moult 

 after they have acquired the use of their wings. 

 The insect which emerges from the split skin of the 

 full-grown nymph is dull in hue, and seems, so to 

 speak, to lack polish. It is, in fact, enveloped in a 

 delicate skin, which is cast off either immediately or 

 in the course of several hours. Thereafter the insect 

 appears in its true colours, having reached its perfect 

 state. 



There are about forty British May-flies, some being 

 very small. One of the commonest is Ephemera 

 vulgata, known to anglers as the " grey drake." 



The seventh order of insects comprises the dragon- 

 flies, and is called Odonata. Its members possess so 

 many distinctive features that they are unlikely to be 

 confused with any other British insects. The large 

 head, which is strongly concave behind, is attached 

 to the thorax by a slender and remarkably mobile 

 " neck," and can thus be turned readily from side to 

 side, enabling the creature to make good use of its 

 huge compound eyes. Dragon-flies depend almost 

 exclusively upon their keenness of vision when hunt- 

 ing their insect prey, which they chase and capture 



