148 FAMILY CYNIPID^. 



the Tenthredinidds. Sometimes there is a projection 

 with a hook-like point at the base not far from the 

 apex. The triangular plate is shaped pretty much 

 as it is in the saw-flies (PL V, fig. 15 d). The two 

 pieces of the sheath are united to form a channel in 

 which the boring part of the ovipositor works ; but 

 it is not so firmly united at the base. Here (PL V, 

 fig. 15 c) there is a horny projection by means of 

 which it is attached to the posterior chitinous piece. 

 The long, thin, wire-like boring pieces are usually 

 toothed at the apex. As with the other Hymenoptera, 

 they are only attached to the triangular piece (PL V, 

 fig. 15, a and &). 



Thus, except in form, there is no radical distinction 

 between the ovipositor of Cynips and the saw-fly 

 beyond the sheath in the former being united. In the 

 different groups, and even species, there is great variety 

 in the form of the chitinous lateral pieces ; and appa- 

 rently their forms may be used advantageously in 

 separating the species. 



The different parts are worked by five muscles. 



The form of the abdomen varies considerably. In 

 some the first segment or petiole forms a long, thin, 

 rod-like peduncle, while in other species it is so thick 

 as to make the abdomen almost sessile. In form the 

 abdomen may be ovate and thick, long, slender, and 

 knife-shaped, or cultriform. It is seldom very much 

 longer than the thorax, and may be even shorter than 

 it, especially in the males. 



The number of the segments apparent is seven in 

 both sexes, with one less on the ventral region in the 

 females, and two less in the males. The relative 

 lengths of the segments vary (see PL XI Y), and this fact 

 is important from a classificational point of view, espe- 

 cially the length of the second and third. Except 

 with Ibalia, either the second or third segment is 

 very much longer than all the others united, and one 

 of them may, indeed, form more than three-fourths of 

 the total length of the abdomen. In the females the 



