OF PHILADELPHIA. 7 



This is often mistiiken for the Hessian fly, in consequence of 

 being found in wheat fields in vast numbers during the devasta- 

 tion committed there by that insect, and many have been deceived 

 by the specious circumstance of its evolution from the pupa it- 

 self of the destroying larva, under their own observation. But 

 the truth is the Ceraphron belongs to that vast tribe of insects 

 included by Linn^ under the Oenus Ichneumon. True to the 

 manners of its kind the parent deposits her eggs Avithin the 

 bodies of the larvae of the Cccidomyia destructor, through a 

 puncture made by her acute oviduct for the plirpose ; the 

 young, when disclosed from the egg, feeding securely within 

 the body of the larva, at length kills it, but not in general until 

 after its change into the pupa state. Protected by this indurated 

 covering, the parasite undergoes its change, and appears in the 

 perfect state, about the latter part of June. It seems probable 

 that this insect prevents the total loss of our wheat crops, by re- 

 straining the increase of the Cecidomyia within certain bounds. 

 The Ichneumon Tipuhr of Mr. Kirby is congeneric with this, but 

 is doubtless specifically distinct. 



[From vol. 2, 1821: pp. 11—14.] 

 Descriptions of the Thysanoarae of the United States. 



Read Nov. 21st, 1820. 



Genus MACHILIS Latr. 



Eyes compound, occupying almost all the head ; [12] abdo- 

 men beneath with an appendage for leaping : tail with three 

 styles, of which one is above the others. 



M. VARIAHILIS. — Superior caudal process more than double 

 the length of the others : false feet bisetous at tip : color cine- 

 reous or iridescent, varied with black. 



Inhabits North America. 



Cabinet of the Academy. 



Body above cinereous, somewhat iridescent, varied with black ; 

 gibbous portion of the body not differently colored ; a more or 

 less regular whitish vitta ; false feet white, hirsute, .setaceous at 

 1821.] 



I 



