Insects and their world 



Fig. 30. A snake-fly, Order Megaloptera 



The external opening, or ovipositor, through which the eggs are 

 expelled varies greatly in different groups of insects, and its shape 

 reveals not so much the relationships of the insect as its breeding 

 habits. The appendages of the eighth and ninth segments of the 

 abdomen — i.e. the structures that on the head have become antennae 

 and mouthparts, and on the thorax have become legs — are modified 

 into lobes and valves to guide the egg on its way out. A simple arrange- 

 ment suffices for all insects that merely drop the eggs on to the ground, 

 among vegetation, or into water : and even for some that place the eggs 

 carefully in a neat stack, e.g. butterflies, mosquitoes, horseflies. 



The Orthoptera show how this simple ovipositor can be adapted 

 for diff'erent uses. The locusts and short-horned grasshoppers merely 

 have the valves of the ovipositor short and strong, and use them to open 

 a way into the soil. The greater part of the abdomen is pushed into the 

 ground, and the eggs are laid at the bottom of the pit. The long-horned 

 grasshoppers, however, have the valves of the ovipositor drawn out into 

 long blades, which interlock and form a compound piercing organ of 

 great strength (Fig. 14). This may be used to pierce the soil, also, but 

 the purpose for which it is adapted seems to be to push into the wrapped 

 tissues of plants, so as to lay eggs between the layers. At the other end 

 of the evolutionary scale of insects, among the Diptera, or true flies, 

 there are some that have a flattened, blade-like ovipositor that is used 

 in much the same way. 



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