376 THE NATURAL HISTORY 



constant vibration, except during the hours of repose, 

 is the conclusion of naturalists who have patiently 

 watched the process of oviposition of several species. 



In the first of the four families under notice, we 

 find a very small curiously formed insect, Evania 

 appendigaster, which is said to deposit its eggs in the 

 egg capsule of the common cockroach. The abdomen 

 in this species is so disproportionately minute, that at 

 first sight it would appear to have been accidentally 

 arrested in its development. We have a humiliating 

 recollection of once placing a specimen of this fly 

 under the microscope, and eventually rejecting it as 

 an insect that, from some cause or other, as we erro- 

 neously thought, had failed to complete its growth. 

 This is a reminiscence of our very early entomological 

 course, another opportunity of examining one would 

 find us better prepared to appreciate it. We have 

 several times netted Fcenus jaculator, another member 

 of this family, with a compressed abdomen growing 

 gradually larger towards the extremity, and a long 

 ovipositor ; it is parasitic on other species of its own 

 order. 



The species of Ichneumon proper which we have 

 seen here and not identified are innumerable, but 

 there are some so remarkable in their appearance, or 

 for their association with other insects that have come 

 under our notice, that we could scarcely fail to recog- 

 nize them, either from verbal description or figures. 

 Conspicuous among these is the Rhyssa persuasoria, 

 the largest of the group, and the species of which we 

 have taken the greatest number of individuals. It is 

 parasitic on the larvae of Urocerus juvencus, piercing 

 with its ovipositor a considerable thickness of solid 

 wood to reach its prey ; accordingly we find both these 

 insects in the same localities and under similar con- 

 ditions. In the summer of 1871, a large scaffolding, 

 consisting of fir poles and deal planks, had been stand- 

 ing several weeks in an outbuilding here, where con- 



