508 HYMENOPTERA 



from above ; in the Xyphidriides it is smaller, and in the middle 

 is entirely vertical in its direction. The mesonotum is moderate 

 in size, and its divisions are delimited by broad vague depressions. 

 The prosternum appears to be entirely membranous, but the 

 prosternal plates (pleura) are large, and meet together accurately 

 in the middle, so as to protect the greater part of the under- 

 surface of the neck. The abdomen is cylindrical or somewhat 

 flattened above ; it has seven dorsal plates in addition to the 

 spine-bearing terminal segment. The trochanters are double, 

 the outer division being, however, short ; the anterior tibia has 

 only one spur ; the anal lobe of the posterior wings is large. 

 The " borer " or ovipositor of the female is a remarkable organ ; 

 it is held projecting directly backwards from the extremity of 

 the body, and has the appearance of being a powerful sting. The 

 apparatus is much longer than it appears, for it proceeds not 

 from the apex of the body, but from the under-surface far for- 

 wards, so that the part exposed is only about one-half of the total 

 length ; it consists of a pair of elongate sheaths, which are easily 

 separable though they wrap together, and enclose a slender tube. 

 This tube is rigid and quite straight ; though appearing solid, it 

 is really composed of two very perfectly adjusted laminae and a 

 third arched piece or roof. The two lower laminae are called 

 the spiculae ; they are serrated or grooved in a peculiar manner 

 near the tip, and although so closely adjusted to the borer or 

 upper piece of the tube as to appear to form one solid whole 

 with it, they are said to be capable of separate motion. In 

 addition to these parts, the termination of the abdomen bears 

 above a shorter piece that projects in a parallel plane, and forms 

 a sort of thick spine above the ventral pieces we have described ; 

 this process is very strong, and has in the middle of its under- 

 face in Sirex gigas a membranous cavity, replaced in S. juvencus, 

 according to Westwood, by a pair of minute pilose styles. The 

 Insect, by means of this powerful apparatus, is enabled to deposit 

 her eggs in the solid wood of trees, in which the larva sometimes 

 penetrates to the depth of eight inches. 



Sirex gigas is one of the most remarkable of our British 

 Insects, but is little known except to entomologists, being usually 

 rare. On the continent of Europe it is, however, an abundant 

 Insect, especially in the neighbourhood of forests of fir-trees, 

 and is a cause of considerable terror. As the Insect is not 



