54^ HYMENOPTERA 



of the sac is obscure, but the embryonic development and the 

 early part of the larval life are passed in the sac, which contains 

 a supply of nutritive matter. The larvae of the Encyrtus are 

 at first entirely confined to this sac, but when they have con- 

 sumed all the nutritive matter in it, they leave it and pass the 

 remainder of their larval and pupal existence in the body-cavity 

 of the caterpillar. They live at first on the lymph (blood) of 

 the Insect, and apparently do it no harm ; nevertheless the 

 strength of the caterpillar is so much enfeebled that it fails 

 to undergo the transformation to a pupa ; the parasites then 

 devour its interior, and use the empty skin as a nidus for their 

 own pupation ; they form cocoons which divide the area into com- 

 partments. Usually the individuals disclosed from one Hypono- 

 meuta are all of one sex, which may be either male or female. 

 Unfortunately the most interesting points of this development, 

 viz. the history of the common sac for the larvae, the nature of 

 the eggs, the earlier embryonic stages, and the nutriment in the 

 sac, are still without elucidation. The account given by Bugnion 

 raises a great desire for information on these points. 



We have in a previous page described the remarkable mode 

 of oviposition of Mantis. Captain Xambeu ^ has made a very 

 curious observation to the effect that a minute Chalcid, Podagrion 

 {Pcdmon) pctchymerus, shelters itself under the wings of the 

 Mantis so as to be in a position to oviposit in the eggs of the 

 latter when it shall be forming its peculiar ootheca. 



The genus Isosoma consists of Insects that differ in habits 

 from their congeners, being phytophagous instead of parasitic. 

 /. tritici and I. hordei live in the stalks of corn, and in North 

 America, where they are known to the agriculturist as joint- 

 worms, are frequently very injurious to crops. They are some- 

 times obtained in large numbers without any males appearing, and 

 a wingless as well as a winged form of the female occurs. Owing 

 to the fact that the allies of these Insects are parasitic, it has 

 been frequently maintained that this may also prove to be the 

 case with Isosoma, but the observations of Eiley ^ and others leave 

 no doubt that the Insects of this genus are really plant- 

 feeders. 



^ JBull. Soc. Ent. France (5) vii. 1877', p. Ixix. ; also Andre, Feuille Natural, vii. 

 1877, p. 136, and Riley and Howard, Insect Life, iv. 1892, p. 242. 



- Insect Life, i. 1888, p. 121, . ; 



