xvi. APPLES OF SODOM. 285 



written owe their existence to the labours of this tiny 

 manufacturer ! 



The insects which produce galls generally belong 

 to the family of small flies called Cynipidce. Their 

 ovipositor is a kind of needle in a sheath like the 

 sting of a bee when in repose, which can be extended 

 to double the length of the insect itself. With this 

 they bore into the tissues of plants and trees, and 

 there deposit their eggs. The instinct which guides 

 each species to select the particular plant or the par- 

 ticular part of the plant best adapted for its operations 

 and for the reception of its larvae, is one of the most 

 remarkable examples of contrivance or design in nature. 

 We see this very specially in the case of the rose- 

 bedeguar, the grub of which lives in the curious 

 structure all the winter, but whose hibernaculum is 

 composed of close non-conducting moss-like bristles, 

 and therefore affords a snug protection from the 

 severity of the weather. This prospective wisdom, 

 however, is not always infallible. Sometimes a case 

 of perversion of instinct occurs. In order to escape 

 from its prison when fully formed, the young insect 

 has in many cases to traverse about half an inch of 

 the walls of the gall-nut, and it has strength for that 

 and no more. But it occasionally happens that two 

 galls are fused together, and the little creature seeks 

 to pierce its way out in the usual way, which happens 

 in this case to be the point of junction between the 

 two nuts. The substance to be traversed at this point 

 is an inch and a half ; the insect has not strength 



