OF INSECTS. 307 



with the basal joint much dilated. Fam. Andrenidce, 

 Apidce. 



In illustrating this order more in detail, we shall 

 first select a characteristic example from the family of 

 the Tenthredinidas.* 



FAM. TENTHREDINID.E. 



This extensive family may be known by having 

 the abdomen sessile, or united by its whole breadth 

 to the hinder part of the thorax, in such a manner, 

 that it possesses but little power of separate move- 

 ment. The maxillary palpi are always six-jointed ; 

 the labial four-jointed ; labium trifid; wings ample, 

 and provided with many complete cells ; females with 

 an ovipositor. 



It is from the use and appearance of the instru- 

 ment just named that these insects are called saw- 

 flies. It is placed at the extremity of the abdomen 

 of the female, on the under side, and is so con- 

 structed, that it combines the properties of a saw 

 and auger. It consists of two plates of the same 

 form and size as two external valves, which serve 

 as a sheath to them, and enclose a short triangular 



* "We purposely exclude from these illustrations the most 

 interesting of all the hymenopterous families, the ApidcB^ as 

 their history is given, in a way commensurate with its impor- 

 tance, in a separate volume. The details there afforded of 

 this characteristic group are so ample, as to preclude the 

 necessity of entering at such length into the generalities of 

 the order in the above sketch, as it would otherwise have 

 been necessary to do. 



