758 CLASS IV. INSECTA. 



of the abdomen, deposits her eggs in the standing timber, and the larvae 

 do much damage by burrowing through the wood. Thus Sirex gigas, 

 British, but much more common abroad, injures fir-trees. S. juvencus is 

 rarer. Tremex columba (Fig. 488) is a well known North American species. 

 Fam. 4. Tenthredinidae. The anterior lobe of the mesonotum is 

 separated from the mesoscutellum by the ingrowth of the lateral pieces ; 

 two spines on each anterior tibia ; pronotum small and fused with meso- 

 notum. The Saw-flies are insects with antennae of varying form, 

 which may have as few as three segments or as many as forty. The well 

 known ovipositor consists of a pair of plates toothed on the lower edge 

 and file-like on the outer surface, protected by a pair of sheaths. 

 This saw pierces into leaves and deposits an egg and a drop of some fluid. 

 The egg is said to grow considerably after being laid. Many of the larvae 

 feed on leaves, some mining in them, others forming galls. Most of the 

 larvae resemble caterpillars in appearance, but they have usually more pro- 

 legs and these appendages have no ring of hooks at the free end. One 

 pair of pro-legs is always on the fifth segment of the body, and this seg- 

 ment in the Lepidoptera is invariably devoid of these structures. Some 

 species have larvae covered with slime like a slug. Cocoons are usually 

 formed, and often in the ground. Athalia spinarum injures turnips, 

 Nematus ribesii currant and gooseberry bushes. Hylotoma rosae injures 

 rose bushes. Many are parthenogenetic. The family is a large one with 

 some two thousand species, which are most common in temperate climates. 

 About four hundred are recorded from our country. 



Sub-order 2. PETIOLATA. 



Abdomen joined to the apparent thorax by a slender waist (petiole), and 

 very movable. The apparent thorax is composed of the true thorax and of 

 the first abdominal segment or propodeum, which is closely united therewith. 

 The petiole is formed of the second, or second and third, abdominal segments. 

 The larvae are white and legless. 



This sub-order has been divided into three series of which the first is 



Series 1. PARASITIC A. 



Trochanter divided into two segments. Ovipositor present in female. 



Fam. 5. Cynipidae. Small, dark insects with very few cells in the 

 wings ; pro- and meso-notum joined and pronotum extending back to 

 insertion of fore-wings ; antennae straight, with twelve to fifteen segments. 

 The Gall-flies have usually a peculiar abdomen in which the tergum of the 

 second or third segment is enlarged and covers in the succeeding segments. 

 The ovipositor is long, coiled up in the body, and of great delicacy. The 

 eggs are laid usually in plants where their presence, or that of some secre- 

 tion, sets up the formation of a gall. In this gall when complete, or even 

 in the bodies of the larvae living in it, other Cynipidae lay their eggs. A list 

 of galls formed by this family is given by Cameron.* One of the commonest 

 species is Rhodites rosae which forms the bedeguar gall on rose-bushes. 

 Many forms are parthenogenetic, and indeed in several species the male is 

 quite unknown. The family is cosmopolitan. 



Fam. 6. Proctotrypidae. Few or no wing-nervures ; pronotum as in 



* Ray Society, iv, 1893 ; v. also Alder, Alternating Generations, Transl. 

 by C. R. Straton, 1894. 



