XX 



INTRODUCTION. 



nasidens, the antennae are to be lengthened out, in order to judge 

 of their terminations, etc. 



For almost all the Solitary Wasps, but particularly for the 

 Odynerus, it is essentially necessary to be able to distinguish 

 clearly the characteristics of the metathorax. Now this cannot 

 be effected otherwise than by separating the wings in a trans- 

 verse direction or rather downward, and by bending the abdomen 

 downward as far as possible, the basis of which will, by tins 

 means, become at the same time easy to study. This posture is, 

 evidently very different from that given to the insects by spread- 

 ing them out. I can affirm, that, whenever one has neglected to 

 give the insect this posture, the metathorax and the abdomen 

 present themselves under the most delusive aspect, and may give 

 rise to the most serious misconceptions. As to describing an 

 Odvnerus properly without having taken this precaution, it is an 

 impossibility. One may, if need be, bend downwards the abdo- 

 men without softening the insect; but then, if the wings are 

 directed backwards, even obliquely, they are enough in the way 

 to produce delusive appearances when the magnifying glass is 



used. 



These observations, true especially for the Odynerus, apply 

 likewise to all the sessile ventrated or semi-pedicellated Vespidae. 



On the Determination of insects. 



There are two manners of proceeding, for the determination of 

 insects. One is analytical, the other synthetical, the former 

 employed by amateurs, the latter by naturalists. The first method 

 consists, when having taken an individual insect, in turning over 

 the leaves of a book in search of the name of the species till one 

 supposes to have hit on the description. This method seldom 

 leads to certainty, often to error. 



The second method requires a collection as numerous as possi- 

 ble in individuals. To procure it, the entomologist ought before 

 all things to devote his efforts to a persevering and active chase 

 after specimens. The greater the number of the representatives 

 of each species, the move certain the determination will become. 

 In difficult performances, we must always begin with the more easy 

 and proceed from the simple to the complex. We must, there- 

 fore, start by separating the most salient and most easy genera to 



