Summary.1Notes are given on the bionomics of certain Chalcididæ, Braconidæ, Proctotrypidæ, and Cynipidæ, especially ofMicrogaster cannexus, Mesochorus pallidus, andAphidiussp.2Microgaster connexus(Nees) is a Braconid parasite on the larvas of the mothPorthesia similis.3Mesochorus pallidus(Brisch.) is a hyperparasite on the larvas ofMicrogasterwhich live inside the larvae of the mothPorthesia similis.4Notes and descriptions of part of the life‐history ofApanteles glomerulus, allied toM. connexus, are also given.5Microgasterlays from sixteen to fifty eggs inside the body of small larvae ofPorthesia similis.In rare cases very few eggs are laid, while in other examples sixty larvae were bred from one parasitized moth caterpillar. Average number about thirty.6The anatomy of the larvae is described. My account of brain, tracheal system, gonads, silk glands, and gut broadly agrees with that of Seurat.7Two tubes, called enigmatic tubular glands, are attached to the vesicle near the gut and pass up the body forwards. They do not, as described by Seurat, connect with the hind region of the gut.8The heart is described; it opens into the last segment of the body, whore it is very wide.9The last abdominal “segment” is expanded into an enormous vesicle, whose structure and minute histology is described.10Two coiled tubes in the vesicle, described for the first time, appear to be excretory in nature.11No Malpighian tubes were found, but it was thought that the enigmatic tubular glands might be modified Malpighian tubes (see pages 411–412).12The gut and fat‐absorption are described. The presence of food in the gut is demonstrated clearly.13The hyperparasite has been shown to oviposit, while the larvalMicrogasteris from one‐third to one‐half full size.14Certain facts with regard to the habits of the hyperparasiteMesochorusare given.15Notes are given on Parasitism and Hyperparasitism among Aphidæ.16Figures of four insects bred from Aphids, and belonging to different Families, are given.17The presence of a peculiar embryonic membrane inAphidiussp. parasitic onAphis pomiis described, and its use pointed out.18The subject of Entomophagous Parasitism in Hymenoptera is fully discussed from the point of view of Microgaste