THE TENTHREDINES. 189 



present a formidable appearance with their exserted ovi- 

 positor. The majority of the larvae of the Tenthredines, 

 however, feed externally upon the leaves of plants, re- 

 sembling much the caterpillars of the Lepidoptera; and, 

 in some cases, they are very destructive to our crops, 

 instanced in the devastation among turnips, caused by 

 what is technically called the blacks, which is the larva 

 of Athalia centifolia. Some of these insects show an in- 

 direct connection with the Cynipsidce, for they form and 

 reside in galls ; but the paramount distinction of the 

 Tenthredines, from all the rest of the Hymenoptera, 

 consists in their possessing, in lieu of an ovipositor, a 

 serrated apparatus formed of two parallel plates, and 

 retractile, when not in use, within a sheath at the apex 

 of the abdomen. When in use, they have an alternate 

 motion, whereby their serrated edge perforates the ve- 

 getable substance to which it is applied, with a longi- 

 tudinal incision, wherein they deposit their eggs. The 

 bodies of these insects are always sessile, and generally 

 robust. Their first division, with knobbed antennse, the 

 Cimbicidce, do not possess the emarginated spine at the 

 apex of the anterior tibiae, which corresponds with a 

 similar excision in the basal joint of the tarsus, and 

 with which the rest of the Hymenoptera cleanse their 

 antennae : in lieu of this, this division has two spurs at the 

 apex of that limb. Many of the species of this group 

 possess also a couple of articulated spurs, placed half 

 way up the tibia : the apex of all these spurs, and the 

 underside of their tarsi, are very frequently also vesi- 

 cular : and, when we take into consideration the greater 

 expansion of their wings, and its more elaborate reticu- 

 lation, and view in conjunction their pedated larvae, we 

 shall no longer cause surprise at considering them 

 aberrant. The more remarkable genera are, Perga, 

 which is exclusively from New Holland, and which 

 broods over its young like a hen over her chickens ; 

 Schizocerus, with its furcated antennae ; Lophyrus and 

 Pterygophorus, which have those organs elegantly pec- 

 tinated in their males; Tarpa and Lyda, with their 



