76 INSECTS 



pollination, at the same time carried also the germs 

 of fire-blight and similar diseases, introducing them 

 into the sensitive tissues of the blossom. It is an old 

 story, of course, that disease organisms frequently find 

 entrance through wounds made by insects; but that 

 is merely putting the insects on a par with other causes 

 that produce abrasions, cuts or bruises: this is a dif- 

 ferent matter, the insect being charged as the active 

 transmitter, much as a fly carries typhoid germs to the 

 human organism. 



Direct plant feeders are found among the Hymen- 

 optera in the Sessiliventres, — "saw-flies" and "horn- 

 tails," — which derive their technical name from the 

 fact that the abdomen is joined to the thorax for its 

 full width and is thus sessile, while in the majority of 

 the species in this order it is stalked or pedunculate, 

 attached at a narrow point only. The saw-flies are 

 somewhat clumsy in appearance and more sluggish 

 than the other Hymenoptera, the body rather uniform 

 in size from end to end, the wings large, with many 

 complete cells, and folded over the back when at rest. 

 They derive their common name from the fact that the 

 ovipositor is made up of parallel blades variously 

 toothed at the edge, by means of which the female 

 cuts a slit or pocket into a leaf, stem or twig, for the 

 reception of an egg. The larvae that hatch from these 

 eggs are caterpillar-like in appearance but have five 

 pairs of abdominal prolegs instead of four or less, as 

 is the case in the true caterpillars. They are mostly 

 feeders on foliage, like the currant worm, and they 

 sometimes appear in enormous numbers ; but they do not 

 often threaten the life of the plant. Some of them only 

 scrape the surface of the leaves like the pear slug, 

 while others eat characteristic holes in them like the 

 blackberry saw-fly. A considerable number are gall- 



