504 IIVMENOPTERA chap. 



Siricidae), and frequently with numerous abdomi^ial legs, 

 lohich are destitute of liooks. Food vegetable. 



The Insects of this sub-Order never exhibit the highly 

 specialised habits and activity of the better known petiolate 

 Hymenoptera. Though the food in the larval stages is always 

 vegetable, there is considerable variety in the larvae and their 

 habits ; some feed in galls, some in the twigs of plants, some in 

 the hard wood of trees and shrubs. The majority, however, live 

 on the leaves of plants. Those that live in wood (Fig. 342, C) 

 resemble in appearance Coleopterous larvae that have similar 

 habits, and those that live on leaves (Fig. 343, A) resemble 

 Lepidopterous larvae that do likewise. There are four families 

 included in the sub-Order, viz. Cephidae, Oryssidae, Siricidae, 

 Tenthredinidae. 



The British Sessiliventres — under the name Phytophagous 

 Hymenoptera — have recently been monographed by Mr. Peter 

 Cameron in a series of vols, published by the Eay Society.^ 

 These contain many figures and many details relating to natural 

 history, in addition to the descriptions of genera and species. 



Fam. I. Cephidae — Stem Sawflies. 



Slender Insects, with weak integument ; free, more or less elongate 

 ■pronotum ; one spine on the front tibia. Larvae living in the 

 stems of plants or in the tender shoots of trees and shrubs. 



The obscure little Insects composing this family have slender 

 antennae of peculiar form, composed of eighteen to thirty joints, 

 two of which are short and stout ; then come several long joints, 

 with more or less power of movement, the terminal portion 

 consisting of an elongate club of many joints with little power 

 of movement. The pronotum is longer than is usual in the 

 Hymenoptera, and instead of Ijeing very closely connected with 

 the mesonotum, it is free and mobile, although its base over- 

 wraps the front of the mesonotum. The median plate {i.e. the 

 dorsal plate connecting the thorax and abdomen) is divided to 

 the base along the middle, the divisions being separated by a 

 membranous piece broader behind ; the anal lobe of the posterior 



1 Mon. Brit. Fhyt. Hym. 4 vols. 1882 to 1893. 



