1% NATURAL HISTORY 



« of its length or more, and narrow the reft. They have 

 K but twenty feet and none in the laft fegment. Thefe 

 " infects fometimes multiply exceedingly on the Pear- 

 " tree, fo that four or five are found on the fame leaf. 

 « I have feen of thefe trees in the month of July without 

 " a green leaf.'t 



This defcription, according fo exactly with the Slug, 

 and the author's mentioning it as a fingular fpecies, in- 

 cline me to believe that it h the only fpecies of this ge- 

 nus which has a mucous coat, and that our Slug-fly is a 

 variety of the Tenthredo Cerafi. The form of the faw 

 in the European fpecies will determine this point. 



This inftrument is a very curious object, and in order 

 to defcribe, it will be proper to compare it with the tenon- 

 faw ufed by Cabinet-makers; which being made of a very 

 thin plate of fteel is fitted with a back to prevent its bend- 

 ing. The back is a piece of iron, in which a narrow and 

 deep groove is cut, to receive the plate, and is fixed; the 

 faw of the Tenthredo is alfo furnifhed with a back, but 

 the groove is in the plate and receives a prominent ridge 

 of the back which is not fixed, but permits the faw to Aide 

 forward and backward as it is thrown out or retracted. 

 The faw of artificers is fingle, but that of the Tenthredo 

 is double, and confifts of two diftinct faws with their backs; 

 the infect in ufing them, firft throws out one, and while 

 it is returning, pufhes forward the other, and this alter- 

 nate motion is continued till the incifion is effected; 

 when the two faws receding from each other, conduct the 

 egg between them into its place. In the artificial faw the 

 teeth are alternately bent toward the fides, or out of the 

 right line, in order that the fifTure or kerf may be made 

 fuffkiently wide for the blade to move eafily : to anfwer 

 this purpofe in fome meafure, in that of the Tenthredo the 

 teeth are a little twifted fo as to (land obliquely with re- 

 fpect to the right line, and their points, of courfe, project a 

 little beyond the plane of the blade, without being lateral- 

 ly bent, and all the teeth in each blade thus project a lit- 

 tle outward; but the kerf is more effectually made, and a 



a 



f Beauraur in Mem. des Infe&es. Tom, 5. Mem. des Mouches a fcie„ 



